Eukaryotic Transcriptional Activator Essay Introduction            Much of what was initially known about transcription came from pioneering prokaryotic transcription studies that followed the1959 discovery of RNA polymerase. During those earlier times, it was presumed that gene structure and transcription in bacteria were practically the same for eukaryotes. This later turned out to be incorrect since eukaryotic DNA assumes higher-order structural forms and transcriptional and regulatory processes in eukaryotes are much more complex. Thus, studies on eukaryotic transcription have become invaluable in further understanding this vital process that regulates gene expression in higher organisms (The Royal Swedish Academy of Sciences 2).            One such study was done by Brent and Ptashne, wherein they investigated which of two proposed mechanisms does GAL4 activate transcription (729). GAL4 is a protein that initiates the transcription of the GAL1 gene in S. cerevisiae, given that a region called UASG or a certain 17-bp sequence (termed “17-merâ€) is present anywhere from 40 to 600 nucleotides upstream of the gene’s transcription start site. The two regions bind GAL4 to activate transcription similarly when inserted upstream in another gene, CYC1 – normally regulated by the two UASs (upstream activation sites) UASC1 and UASC2, which bind certain cellular proteins (in Brent and Ptashne 729).            GAL4 is thought to activate transcription either by a) binding to DNA and stabilizing unusual DNA structure so that protein binding near the transcription site is promoted; or b) binding to DNA without disturbing its structure and activating transcription by getting in contact with other proteins. Based on earlier lambda experiments that involved mutant repressors which, operating via mechanism b above, can bind DNA but are unable to activate transcription because the amino acids in the region thought to contract RNA polymerase were altered, Brent and Ptashne tried to determine the domains responsible for GAL4’s DNA-binding and activator functions. For this purpose they used LexA-GAL4, a new protein construct having the DNA-binding specificity of LexA, an E. coli repressor protein whose amino-terminal domain binds to operator regions to repress gene expression (729). It was found that LexA-GAL4 functions in the same manner in E. coli, but activates transcription in yeast if and only if, a lexA operator is likewise present near the transcription start site (730). Data Analysis            The synthesis of LexA-GAL4 in bacteria and yeast was facilitated through the use of plasmids. The gene for LexA-GAL4 is the combination of the E. coli DNA fragment that codes for the 87-residue amino-terminal of LexA, and the S. cerevisiae fragment coding for the 807-residue carboxy-terminal of GAL4. Figure 1a (see Tables and Figures) shows the DNA sequence and corresponding amino acids coded in the LexA-GAL4 fusion junction while b and c respectively show plasmid 1109, whose LexA-GAL4 synthesis is regulated by the tac promoter, and 1027, regulated by the ADH1 promoter (Brent and Ptashne 730).             LexA-GAL4’s repressor activity in E. coli was demonstrated by two experiments. Table 1 summarizes the results of the first experiment on a bacterial strain wherein a lacZ gene was adjoined to the lexA promoter. LexA autorepresses its own transcription so the strain used carried a mutant, nonfunctional lexA gene. Plasmids were then used to synthesize different regulatory proteins after which repressor activity was measured by the amount of b-galactosidase produced by lacZ. The results show that LexA-GAL4 transcription repression from the lexA promoter was comparable to that of LexA. Meanwhile, Figure 2 shows the results of the second experiment which made use of the fact that certain LexA-repressed genes need to be expressed for cells to recover from DNA damage. That is why, cells with a mutant LexA that is able to bind to the operator but can’t be deactivated through proteolysis exhibit UV sensitivity. Figure 2 shows the survival rate of E. coli cells depending on the regulatory proteins synthesized by corresponding plasmids. As with the first experiment, LexA-GAL4 showed a similar repressor action as with LexA so that E. coli cells that had them were markedly UV-sensitive compared to cells that had no regulatory protein or had the l repressor which does not recognize the lexA operator and hence has no regulatory effect on transcription (730-731).            In contrast to its action in E. coli, LexA-GAL4 acts as a transcriptional activator in yeast when a lexA operator is present. Plasmids were used to transform one group of GAL4+ cells into producing LexA-GAL4 and another to produce native LexA. Both groups were then further modified to carry a gene made from the fusion of either GAL1 or CYC1 and lacZ, and either UASG, the 17-mer, UASC1 and UASC2, a lexA operator, or none of these upstream of the gene (see Figure 3). From the CYC1-lacZ gene results in Table 2, it can be seen that whereas LexA repressed b-galactosidase production, LexA-GAL4 activated transcription but only when there is a lexA operator upstream. Transcription appeared to be stimulated more when the operator is nearer the transcription start site. Conversely, transcription was markedly hindered in the glucose medium (731-732) which is consistent with previous observations that GAL4 is only active when cells are grown on a galactose medium but is inhibited in the presence of glucose (729). Table 3 shows the same trend in LexA-GAL4 activity with the GAL1-lacZ gene. In fact, LexA-GAL4’s dependency on the presence of a lexA operator to activate transcription was also emphasized in similar experiments using strains having either a gal4 gene point mutation or a gal4 deletion, wherein LexA-GAL4 activated CYC1-lacZ and GAL1-lacZ transcription only when an operator was present and likewise, was dependent on operator proximity to the transcription start site. In these experiments, LexA-GAL4 failed to stimulate b-galactosidase production even in plasmids bearing UASG or the GAL1-lacZ gene, nor was it able to compensate for the absence of wild-type GAL4 when no operator was present (731-732). Comparison of LexA-GAL4-stimulated GAL1-lacZ transcription with that in a plasmid bearing wild-type UASG showed that the 5’ ends of the RNAs made were the same (Figure 4). However, it is not yet clear why the amount of transcripts produced was only 5% of that which was expected based on b-galactosidase measurements (731). The reduced activity of GAL4 on glucose media is attributed to the association of the GAL4 C-terminus with the inhibitory protein GAL80, thus hindering efficient binding with UASG (729). The results in Table 4 indicate that the LexA-GAL4 C-terminus likewise associates with GAL80. A glucose medium was used to grow GAL4-producing cells that had UASG but no lexA operator upstream of a GAL1-lacZ gene. Results suggest that LexA-GAL4 proteins, in the absence of an operator to bind to, are free to interact with GAL80 and consequently facilitate transcription by leaving wild-type GAL4 to bind to UASG (732-733).            Figure 5 shows a spliced yeast gene and a derivative wherein a lexA operator was inserted into the gene’s intron. This was done to test whether LexA-GAL4 can also activate transcription if the operator is downstream of the normal transcription start site. UASG was present upstream but a gal4 strain was used so no GAL4-stimulated transcription would occur and b-galactosidase production would be purely dependent on LexA-GAL4. From the results in Table 5, it may be seen that LexA-GAL4 was able to stimulate transcription only when there’s an operator in the intron, though b-galactosidase production was only 4% as much of that resulting from transcription from UASG in a GAL4+ strain (733).            The essence of this study’s findings is depicted in Figure 6, which shows that the hybrid protein LexA-GAL4 can successfully stimulate transcription in yeast but only in the presence of a lexA promoter upstream (733). Tables 2 3 and more importantly, the parallel experiments with the GAL4-expression impaired strains (731-732), best illustrate LexA-GAL4’s strict requirement for the presence of an operator in order to activate transcription. Conclusions            Through the series of experiments done, Brent and Ptashne were able to gather data attributing activator function to GAL4’s C-terminus, consequently suggesting that activation by GAL4 is more probably achieved by its interaction with other proteins rather than by binding to UASG and then perturbing DNA structure. Since LexA-GAL4 successfully activated transcription without binding to UASG, a change in structure doesn’t appear to be crucial for transcription to occur (733). Though the results of the experiments were per se quite conclusive, they are rather indirect evidence for the GAL4 mechanism being put forward. A probably more direct proof is offered by the Keegan, Gill and Ptashne study mentioned which claims that another hybrid protein having the amino terminal of GAL4 binds UASG but fails to activate transcription, likely because the C-terminus is that of b-galactosidase which functions differently (733). This study has successfully illustrated the synthesis of hybrid proteins that can be used for exploring further not just the activator function of other eukaryotic regulatory proteins (734), but on the whole, transcriptional and regulatory processes in various other eukaryotic organisms. Good follow-up studies would therefore be a structural study to determine whether no change in DNA structure is indeed involved in GAL4 activity and more generally, the application of the methods and concepts learned here to other eukaryotic genes and their known regulators so as to perhaps be able to establish whether a mechanism similar to that proposed for GAL4 is also in play. Both ultimately can help to build a general but detailed picture that will allow for a deeper understanding of eukaryotic transcription and regulation of gene expression.
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The Reality Of Platonic Relationships Sociology Essay Romantic relationships are characterized by feelings of passion, emotional reactions and physical attraction; and platonic relationships are characterized by the absence of physical attraction, passion or sex (Sippola, 1999). These two characterizations are very important for the scope of this paper because both are crucial to answer the question, Can men and women really be just friends? In the magazine Psychology Today, Clifford Lazarus wrote an article with an explanation to this question. Lazarus contends, for the most part, purely platonic relationships for heterosexual men and women are a myth (Lazarus, 2010). To support his contention, he refers to the reflexive nature of men and the reflective nature of women. Lazarus refers to a sexual desirability reflex, which men demonstrate towards women in prime reproductive age. This reflex suggests the immediate thoughts of males when first encountering females are whether or not he would like to have sex with her (Lazarus, 2010). Although, it is argued that females may exhibit the same thoughts, although not as frequently as with males, they tend to quickly move past this reflex. On the other hand, women generally want to determine the suitability of a potential partner. This suitability is referred to as a desire to look for potential long term, socioeconomic stability with a partner (Canary Dindia, 1998). Women therefore, tend to be more sexually reflective and choosier than males, while males tend to be more sexually reflexive than women. These reflexive and reflective drives can be linked to evolutionary theories. Males have an indefinite amount of sperm while females only have a predetermined amount of eggs for her life span (Lazarus, 2010). This suggests an explanation of why males may exhibit the above mentioned reflex more than females, and why females exhibit a determinable reflective drive. This article therefore concludes that purely platonic relationships in cross-sex friendships do not exist. The purpose of this paper is to compare and contrast the conclusion of the Psychology Today article with scholarly research to determine if purely platonic cross-sex friendships can exist between heterosexual men and women. It is important to indicate that the articles conclusion assumes that a purely platonic relationship exists when both people in the relationship have never considered having a romantic relationship with each other. Through sexually charged flirtatious behavior and evolutionary theories, the first part of this paper will provide support for the articles conclusion that purely platonic cross-sex friendships are not possible. However, the second part of this paper will present evidence denouncing the preceding hypothesis by means of costs, romantic intentions and reasons to stay platonic. Flirtatious Behavior Both romantic and platonic relationships report flirtatious activity although frequencies in flirtatious behavior may differ (Egland, Spitzberg, Zormeier, 1996). Some examples of flirtatious behaviors include looking your friend or partner up and down, gazing in their eyes and smiling suggestively. When comparing results of the platonic cross-sex relationships to the romantic cross-sex relationships, platonic relationships engaged in flirtatious activity nearly as much as romantic relationships (Egland, et al., 1996). This finding bolsters the view that even in platonic relationships, flirtatious behavior is expressed. Furthermore, flirtatious behavior may be sexually charged. According to Henningsen, Braz, and Davies (2008), people engage in flirtatious behavior for six main reasons. First is sexual motivation, referring to ones desires to engage in sexual acts. Second, an individual may be relationally motivated, with the intention of moving from a platonic relationship to a romantic relationship. Third is fun motivation, referring to flirting to gain sexual excitement or thrill. Fourth is exploring motivation, referring to flirtatious behavior of platonic relationships to explore and see if positive feedback comes from the other person. Fifth is esteem motivation, which remarks on how gaining positive feedback from flirting may boost self esteem or arousal. And finally people flirt for instrumental motivation, which is flirting for possible access to rewards. Flirting is the primary apparatus to signal sexual and romantic accessibility (Guererro Chavez, 2005). All of the reasons people may flirt are charged with motives other than being platonic. Flirtation can be described as a subcategory of social-sexual communication (Henningsen, et al., 2008, p. 2). These social-sexual communications carry the connotation of being sexually charged, suggesting one person may have had sexual or romantic thoughts at one point in time in the relationship. This suggests that flirting is associated with sexual desire, or reasons other than what constitutes a platonic friendship (Henningsen, Braz, Davies, 2008). Flirtatious behavior is often intended to be interpreted in a way that carries sexual motive (Henningsen, et al., 2008). This implies that those in platonic relationships have an intended purpose or conscious motive to engage in it. For instance, platonic relationships that do not want to turn romantic voluntarily do not engage in flirtatious behavior (Guerrero Mongeau, 2008). This suggests that platonic relationships may be conscious of flirting, thus indicating that people engage in flirting through a particular motivation; in these instances a sexually charged motivation. Since platonic relationships do engage in flirtatious behavior with one another, there is reason to believe that the flirtatious behavior is sexually charged Furthermore, men may interpret expressed behavior from women differently than from what women intend. If women are not voluntarily trying to give flirtatious signals or signs of flirtatious behavior, men are much more readily apparent to interpret non-flirtatious signals as flirtatious (Canary Dindia, 1998). Therefore, even in an apparently platonic friendship, men may be misinterpreting these non-flirtatious signals as flirtatious, and therefore sexual as well, even if there is no intension to communicate flirtatious behavior. This implies even in some apparently platonic relationships, certain behaviors may signal signs of sexual desire unintentionally. CHECK THESE PRECEDING 3 PARAGRAPHS Evolutionary Views According to evolutionary theories, flirtatious behavior is contingent upon a desire to procreate (Canary Dindia, 1998). As mentioned in the article, men have a type of reflexive drive and women have a type of reflective drive (Lazarus, 2010). From an evolutionary stance, a look into interactions between men and women will reinforce these reflexive and reflective drives. Reflective and Reflexive Behavior Women are more likely to choose a partner or mate who exhibits status and resources, therefore being more reflective than males (Lazarus, 2010). Women are generally more interested in men with high resource potential (Canary Dindia, 1998). This indicates why women focus on a long term stable relationship; one which is able to support their offspring. On the other hand, men are much more likely to approach women who display more signs of flirtatious behavior (Canary Dindia, 1998). This indicates mens reflexive drive, indicating sexual thoughts or interest upon initial encounters (Lazarus, 2010). Interests of men and women vary depending on age group. Males prefer younger women, while women prefer older males as age ascends. Women tend to be more fertile when they are younger, while men tend to be more economically sufficient and successful as they grow older (Alterovitz Mendelsohn, 2009). This suggests men being more concerned with the fertility of women by preferring younger mates, while women reported being more concerned with male socioeconomic status, indicated by selecting older men (Alterovitz Mendelsohn, 2009). Parental Investment Theory Additionally, the female perception of older males having the resources to provide for their offspring and males having the impression to mate with a fertile female is consistent with the evolutionary theory of parental investments. Under parental investment theory, the investments of men and women differ. For example, a women needs to carry the offspring. On the other hand, men could technically end their investment of the offspring immediately after conception. As referenced by Tafoya (2006), womens potential for reproduction after conception is inhibited, while on the other hand men as quoted by Lazarus (2010), have their sperm constantly replenished. Furthermore, because of the paternity uncertainty hypothesis, a man can never know with absolute certainty that a child is his. On the contrary, even though the mother may not know who the father of her child is, this hypothesis holds that she will know for certain that she will pass her genes on to her offspring (Tafoya, 2006). Considering this hypothesis and the theory of parental investments, the reflexive nature of men and reflective nature of women are explained. A males reflexive drive can be explained since males never know if the child is theirs with absolute certainty and their investment need not go beyond conception (Tafoya, 2006). Therefore, males seem to exhibit lesser commitment, reinforcing their reflexive tendencies. Additionally, men are more likely to accept a short term mate of any overall quality than women. For instance, it is more probable that men rather than women select a short term mate whose overall qualities such as wealth, status and attractiveness are lacking. Men are also more likely than women to have a one night stand or participate in an affair (Li Kenrick, 2006). On the other hand, women know their genes will be passed on and are making more of a sacrifice from an evolutionary standpoint by the cessation of their potential reproduction. This indicates that females may be more selective about their mates as indicated in the article by reflective drives. Furthermore, women prefer resources and status when looking for a short term mate more than males. In fact, women prefer the same qualities in their short term mates as they do in their long term mates (Li Kenrick, 2006). This implies women exemplify this reflective drive in support of a potential parental investor, that being the potential mate. It is shown that mating as well as parenting is essential to success of offspring, which helps to explain the characteristics of these reflexive and reflective drives (Tafoya, 2006). However, evolutionary views not limited to parental investment theory. Friends with Benefits and Biosocial Theory Evolutionary theories are evident in friends with benefits relationships. Friends with benefits refer to non-romantic or platonic relationships who engage in sexual activities (McGinty, Knox, Zusman, 2007). Friends with benefits is not just a trend, but also is commonly engaged in. Nearly 60% of undergraduates reported having had an experience with a friends with benefits relationship (McGinty et al., 2007). This reinforces the instinctive sexual activity and sexual behavior with the opposite sex. Biosocial theory of evolution may inquire more deeply as to why friends with benefits occurs. Biosocial Theory predicts human behavior by looking to a persons genetic predisposition and their environment. Women show to be more emotionally involved in a friend with benefits relationship than men. Because women emphasize emotional attachment, it is argued that women do so in order to have a stable relationship (McGinty et al., 2007). In having a stable relationship, women need to rear their offspring, thus suggesting why women are more emotionally concerned with friends with benefits relationships than men. On the other hand, men are more sexually focused with the relationship. At times, men are shown to be involved in multiple friends with benefits relationships, thus strengthening the point that men exhibit a reflexive drive (McGinty et al., 2007). Furthermore, Schneider Kenny (2000) surveyed how rewarding and costly people see an opposite-sex platonic friendship. Sexual access was reported as a potential benefit of being in a cross-sex friendship, as well as a reported cost. For example, men may be friends with women as a means to gain sexual access, however, men report having less sexual access than women. This suggests men are more concerned with sexual access than women (Bleske Buss, 2000). This reinforces the idea of the reflexive nature of men. However, women are reported to be benefited when protected by an opposite sex friend. Though this is not shown to what extent this suggests a positive cue for women as mate potential, it has been suggested in a comparative study that males who protect their friends actually gain more sexual access. This was evident in a study of baboons, where the males protect the feeding grounds, and in return the female gives them periodic sexual access; therefore suggesting mens evolutionary drive for protecting women (Bleske Buss, 2000). Flirtatious behavior and evolutionary views support the reflexive and reflective tendencies of males and females, respectively. This suggests that men and women in platonic cross-sex friendships engage in sexually charged behavior. The preceding information also supports, as the article contends, that platonic relationships may not be feasible simply because of evolutionary drives (Lazarus, 2010). Although these findings reinforce the idea that purely platonic relationships do not exist, there is information to believe otherwise. The following research in categories of similar costs, romantic intent, and reasons to stay platonic indicate evidence against the preceding research, contending there may be reasons platonic relationships can exist without having intent for or a transition to romantic relationships. Similar Costs and Status Males and Females do not differ in how costly it is to be denied sex from the person in the friendship; the potential for rejection is perceived as low in cost for both sexes (Bleske Buss, 2000). This suggests that men and women may be able to be friends without worrying about sexual access. However, this information does support males and/or females think about sex. Since the potential cost for rejection was low, this implies the male and females evaluated each other before making the decision to become romantic (Bleske Buss, 2000). Therefore, this seems to be more closely related to the conclusion in the article, and more supportive of reflexive and reflective behavior than not. Even so, the status of the relationship may have an effect on the friendship. Although, ex-romantic partners report wanting a platonic relationship to turn romantic once again, a friend who has always been platonic would not want the relationship to turn romantic (Schneider Kenny, 2000). This indicates that how a relationship is initiated may have an actual impact on the relationship. Platonic friendships therefore, may exist depending on past experiences with the individual. This undermines the contention that platonic cross-sex friendships can never be platonic, since past experience can have an impact. Romantic Intent Romantic intent was not classified in the above article Why Men and Women Cant be Just Friends. Romantic intent can vary and impact relationships differently. In the strictly platonic relationships, cross-sex friends reported less contact, flirtation and activity compared to romantic relationships. Arguably, strictly platonic friendships do not flirt, touch and spend as much time with one another relative to mutually romantic relationships, possibly because doing so may jeopardize the friendship (Guererro Chavez, 2005). Furthermore, long term strictly platonic friendships can move past initial romantic intent. Friendships in the long term are shown to use maintenance behaviors such as less contact and flirtation as a means to not potentially ruin the platonic friendship (Guererro Chavez, 2005). These finding suggests strictly platonic and mutually romantic relationships do vary with romantic intent, and thus may not perceive one another as anything more than platonic friends. Reasons to Remain Platonic There are six motives as to why relationships should remain platonic. To safeguard the relationship, lack of or no attraction, network disapproval, third party, risk aversion and timeout. This order with safeguarding the relationship being most important implies that there is an intrinsic reason for relationships to remain purely platonic. The rewarding nature of the relationship may be seen as more rewarding than a relationship moving towards one that is romantic or sexual. For instance, a reward in a platonic relationship is the ability to share emotion and/ or gain support about external situations; the ability to disclose in the relationship. On the other hand, less rewarding factors may direct people to remain platonic as well. For example, one may feel that the friend in the relationship is not attractive, or one may not want to expose oneself to possible emotional instability (Messman, Canary, Hause, 2000). Thus, research suggests cross-sex platonic relationships may have strong reasons for existing. Furthermore, all platonic friendships may not be sexually charged. The sexual challenge in cross-sex friendships, which refers to men and women being hardwired to be sexually attracted to one another, is said to only occur in a minority of cross-sex friendships. Furthermore, the sexual challenge may be linked to attraction of the spirit, rather than of the body. Thus, reinforcing that sexual challenges may not be accurately represented when referring to the sexual desire of men and women (Messman et al., 2000). Conclusion Flirtatious behavior and evolutionary theories strongly support the idea that there cannot be purely platonic relationships as indicated in the article. However, alternative research suggests platonic friendships may be possible; similar costs, subjective romantic intent, and reasons to remain reasons to remain platonic are evidence that friendships have some incentive to remain purely platonic. Although there is support for both sides, the underlying question is whether men and women together can have purely platonic friendships. Flirtatious behaviors as well as the evolutionary theories of biosocial and parental investment demonstrate that cross-sex platonic friendships are challenging. The majority of the information in the Why Men and Women Cant be Just Friends article does give credence to the majority of these findings. Although in light of these findings, the article seems to be narrow in its evaluation. The main point of the article contends that platonic relationships do not exist because of evolutionary reasoning based on reflexive and reflective drives (Lazarus, 2010). On the other hand, the article does not account for romantic intent, a significant part of relationships. The article assumes based on the first meeting of men and women that there are uncontrollable biological reactions which occur. Although these reactions tend to happen, the article should still account for the past and present status of the relationship, as well as each persons intent to whether or not they want a platonic or romantic friendship. Since the article fails to account for this romantic intent of a males and females, it therefore neglects the possibility of differences in perception; that is, how people view each other based on their past experience with that person (Messman et al., 2000). Moreover, long term platonic friendships vary in their romantic intent depending if maintenance behaviors are used. For instance, in a relationship that has always been platonic, both persons will use more maintenance behaviors to preserve their platonic friendship, in order to safeguard the friendship from moving towards romanticism. However, maintenance behaviors are also shown not to be useful. For instance, one of the people in the relationship may be denied a desired sexual progression (Guererro Chavez, 2005). Although there can be changes made to the article, the underlying argument is supported by the majority of research. Assuming a purely platonic relationship to be a cross-sex friendship where neither party has the thought of addressing a romantic relationship, or having desire for sexual activities; the existence of purely platonic relationships is slim. Platonic relationships engaging in flirtatious behavior carry a sexual connotation (Egland, et al., 1996). This implies that males and females even in platonic relationships may exhibit these reflexive and reflective drives. Furthermore, the differing parental investments for males and females bolster the sentiment regarding reflexive and reflective drives; this concerns why males invest less in their relationships while females invest more in their relationships (Li Kenrick, 2006; Tafoya, 2006). Additionally, the biosocial theory suggests evolutionary underpinnings consistent with reflexive and reflective behavior; these include sexual behavior in friends with benefits relationships and behaviors of rewards and costs. Therefore, the article and the preceding findings suggest that the existences of purely platonic cross-sex heterosexual relationships are unlikely.
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