8. Yeast genes have cis-acting elements upstream oftheir promoters, similar to enhancers, called upstreamactivating sequences or UASs. Several target genes involved in galactose utilization are regulated by onetype of UAS called UASG, which has four bindingsites for an activator called GAL4. Two target genesregulated by UASG are GAL7 and GAL10. The GAL80 protein is an indirect repressor of GAL7 and GAL10transcription: At UASG, GAL80 binds to GAL4 protein and blocks GAL4’s activation domain. In thepresence of galactose, GAL80 no longer binds GAL4.In which gene(s) (GAL4 and/or GAL80) shouldyou be able to isolate mutations that allow the constitutive expression of the target genes GAL7 andGAL10 in the absence of galactose? In each case,what characteristics of the protein would the mutationdisrupt?

Many genes whose expression is turned on by DNAdamage have been isolated. Loss-of-function mutations in the lexA gene lead to the expression of manyof these genes, even when there has been no DNAdamage. Would you hypothesize that LexA protein isa positive or a negative regulator? Why?

LysR regulators like llvY repress transcription from their own promoters. This is called a negative feedback loop. Why might negative feedback be a good way to control expression of a transcriptional repressor? This type of negative feedback loop ensures that ilvC transcription will always be repressed when llvY levels are low, and ilvC will be transcribed highly when llvY levels are high. This type of negative feedback regulation ensures that ilvY is never transcribed. Since llvY is a transcriptional repressor, it will slow down cell growth by blocking transcription. So, llvY represses it's own transcription so that no llvY can ever be made, and the cell can grow. This type of negative feedback loop ensures that there is always a moderate amount of llvY. When IlvY levels fall too low, transcription from the promoter will increase since IlvY won't be able to repress it's own promoter. This negative feedback also ensures that IlVY levels don't rise too high - when llvY levels are high,…

1. Draw a simplified model of a cis-regulatory element with multiple trans-acting factors up-regulating gene expression. Your simplified model must include: a double-stranded DNA molecule labeled with its appropriate orientation (3' and 5', etc.), an area of DNA highlighting the gene of interest to be transcribed, a highlighted area showing the promoter region, one cis-regulatory element upstream of the promoter with its specific transcription factor • RNApol + a general transcription factor + a TATA binding protein all bound to the appropriate area (think about where these bind before transcription starts), an upstream enhancer with its transcription factor bound to it, • and finally the TSS. All parts must be labeled and in the correct area to earn full credit. **I suggest using different colors for this drawing problem**.