Your laboratory investigates utilization of the sugar \"comatose\" by yeast. Thi

Question

Your laboratory investigates utilization of the sugar "comatose" by yeast. This table shows that the expression of comatose kinase (CK), an enzyme required for comatose degradation, is negatively regulated by glucose. You've isolated four mutations (com-1, com-2, com-3, com-4) that affect regulation of CK expression. Your genetic analysis indicates that com-1 and com-3 are linked to the CK structural gene, and that com-2 and com-4 are unlinked to each other and also unlinked to the CKgene. The quantity of comatose kinase expressed by haploids and by heterozygous diploids is shown in the table.

Part A - One of the mutations affects an enhancer to which a positive transcription factor binds. The enhancer is located upstream of the CK gene and is required for induction of ?CK? expression by comatose. The mutation destroys function of the enhancer.

Which mutation is this?

Part B - One of the mutations affects the trans-acting positive transcription factor discussed in Part A. The mutation destroys function of the transcription factor.

Which mutation is this?

Part C - One of the mutations affects a silencer to which a negative transcription factor binds. The silencer is located upstream of the CK gene and is required for repression of CK expression by glucose. The mutation destroys function of the silencer.

Which mutation is this?

Part D - One of the mutations affects the trans-acting negative transcription factor discussed in Part C. The mutation destroys function of the transcription factor.

Which mutation is this?

com-1 ?com-2 ?com-3 ?com-4 Comatose Kinase Enzyme Levels (in relative units) carbon source glucose genotype glucose comatose comatose wild-type com-1 com-2 com-3 com-4 com-1/+ com-2/+ com-3/-+ com-4/-+ 1,000 20 1,000 1,000 20 1,000 1,000 1,000 1,000 20 1,000 20 1,000 20 1,000

Explanation / Answer

Part A. Com-4

When the carbon source comatose is present, the expression of CK is 1000 units in wild type whereas it is only 20 in Com-4 mutants.

Part-B: com-2. The relative activity of the enzyme is reduced when combination of glucose and comatose are present

Part-C: Com 3

Part-D: Com1. In the presence of negative transcription factor (as in wild type) the levels of CK enzyme are very less, where as in heterozygous diploids, the concentration is pretty high.

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