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Simon Fraser University
Biological Sciences
BISC 202
Timothy Swartz

12Regulation of Gene Expression in Eukaryotes WORKING WITH THE FIGURES1 In Figure 124 certain mutations decrease the relative transcription rate of the globin gene Where are these mutations located and how do they exert their effects on transcriptionAnswer The mutations that decrease transcription all fall within the promotorproximal and promotor elements which are located upstream of the coding region and serve as binding sites for RNA PolII and general transcription factors Mutations in these regions hinder proteinDNA interactions and thereby reduce transcriptionThe figure shows that this reduction can be substantial when even a single nucleotide is changed 2 Based on the information in Figure 126 how does Gal4 regulate four different GAL genes at the same time Contrast this mechanism with how the Lac repressor controls the expression of three genesAnswer Gal4 has a DNA binding domain that targets a specific UAS sequenceThis sequence is present in the enhancer region of four different GAL genesGal4 is able to activate transcription from the four separate GAL promoters through its capacity to bind with all four UASsIn prokaryotes the Lac repressor controls expression of three genes by blocking or unblocking access of RNA Polymerase to a single promotor region that is common to all three genesThese two regulatory systems are similar in that genes involved in metabolic pathways for a specific sugar are coordinately induced by the presence of the sugar 3 In any experiment controls are essential in order to determine the specific effect of changing some parameter In Figure 127 which constructs are the controls that serve to establish the principle that activation domains are modular and interchangeableChapter Twelve 326 Answer Controls lack certain experimental treatments to establish a baseline for resolution of treatment effectsIn this figure one control we could call this a positive control is illustrated in panel a which demonstrates normal expression of the lacZ reporter when the Gal4 DNA binding domain and activation domain are both present The other set of controls negative controls consists of DNA binding domains from LexA and Gal4 that lack activation domainsThey show that in the absence of an activation domain the reporter gene lacZ is not expressed Together these controls allow a robust interpretation of panel d where a LexAGal4 hybdrid is used which is that the match between the activation domain and the promotor region activates transcription independently of the DNA binding domain 4 Contrast the role of the MCM1 protein in different yeast cell types shown in Figure 1210 How are the aspecific genes controlled differently in different cell typesAnswer In a cells MCM1 protein acts alone to activate aspecific genesspecific genes are not activated because the necessary helper proteins are notpresent in a cellsIncells 1 protein binds with MCM1 to activate specificgenes Another protein 2 binds with MCM1 to prevent activation of a specific genesIn a hybrids neither the aspecific nor the specific genesareactivated because MCM1 is prevented from activating aspecific genes bythe presence of 2 protein and 1 which is necessary for activation ofspecificgenes is repressed by an a12 complex In a cells aspecific genesareactivated by MCM1 aloneIn other cells the activation of aspecific genesis prevented by 2MCM1 5 In Figure 1211b in what chromosomal region are you likely to find the most H1 histone proteinAnswer Figure 1211c illustrates variation in the density of condensation along a chromosomeH1 histone is evenly distributed along an uncondensed chromatin fiber shown in 1211a and the density increases with the increasing condensation of the chromosome The most H1 histone would be found where the chromosome is most condensed in the heterochromatin depicted in red in the figure hat is the conceptual connection between Figures 1213 and 12196 WAnswer Figure 1213 depicts a general model for how chromatin remodeling can uncover previously hidden regions along the chromosome Figure 1219 shows the details of how SWISNF participates in chromatin remodeling to expose the TATA box of interferon allowing binding of the TATA binding
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