Vallier, L.G. & M. Carlson (1994) Synergistic release from glucose repression by migl and ssn mutations in Saccharomyces cerevisiae. Genetics 137: 49-54.

1. Answer using the results in Table 2.

(a) Which piece(s) of data allow the authors to conclude 'migl is much less effective than ssn6 in relieving glucose repression'.

(b) Which mutation is epistatic to the other ssn6A9 or migl A2::LEU2 and why?

2. Diagram the cross (MCY1773 x MCY1943) used to demonstrate that SSN1 and M1G1 are different names for the same gene. Show the genotype and phenotype of the parents and the diploid.

Use the data shown in Figure 2 to answer the following questions, (a) For this experiment, the cultures were grown in repressing conditions. What does the term 'repressing conditions' mean?

(b) Why were the cultures grown in minimal medium lacking uracil (SM-Ura or SC-Ura)?

(c) What is the level of invertase expression in the wild-type, migl, ssn4, and migl ssn4 double mutant strains? Give numbers.

(d) Describe why this is an example of enhancement.

4. Answer the following questions using the results reported in Table 4.

(a) How do the strains used in Table 4 differ from those used in Figure 2?

(b) Summarize the evidence that migl and ssn4 exhibit enhancement with regard to the ability of these mutations to suppress snfl.

5. The authors examined the relationship of the Migl and Ssn6 proteins by examining the genetic interaction of mutant alleles of MIG1 and SSN6. Their model is that Miglp binds to the SUC2 promoter and to Ssn6p and Tuplp thereby 'tethering' the Ssn6p-Tuplp repressor complex near the transcription initiation site and inhibiting transcription.

(a) This model suggests that Miglp and Ssn6p function in the same signaling pathway. What evidence do the authors present in support of this? Hint: look in Table 2.

(b) What evidence indicates that migl and ssn6 mutations do not exhibit enhancement of the glucose insensitive phenotype? Hint: look in Table 4.

(c) What evidence indicates that migl and ssn6 mutations do not exhibit enhancement with regard to their ability to suppress snjT! Hint: look in Figure 2.

6. The genetic interaction between migl and ssn6 is functionally different from the genetic interaction between migl and the other ssn mutations.

(b) Using the diagram below and arrows (-to represent positive regulation and perpendicular lines (-1) to represent negative regulation, diagram the genetic relationship of SNF1, SSN6, MIG1, and SSN4.


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