The SOS repair genes in E. coli are negatively regulated by the lexA gene produc

Question

The SOS repair genes in E. coli are negatively regulated by the lexA gene product, called the LexA repressor When a cell sustains extensive damage to its DNA, the LexA repressor is inactivated by the recA gene product (ReCA), and transcription of the SOS genes is increased dramatically. One of the SOS genes is the uvrA gene. You are a student studying the function of the uvrA gene product in DNA repair. You isolate a mutant strain that shows constitutive expression of the UvrA protein. Naming this mutant strain uvnAC, you construct the following diagram showing the lexA and uvrA operons. Which two mutations would result in a uvrA constitutive phenotype, i.e., a phenotype in which the UvrA protein is expressed all the time? Indicate the actual genotypes involved. Select the two comect answers. mutation in uvrA-(mutation in the gene itself) mutation in lexA- (mutation in the repressor gene product) mutation in uvrA^O. (mutation in the operator) mutation urvA^P. (mutation in the promoter)

Explanation / Answer

two correct answers are 2 & 3

Explanation

2. as mutation in lex A lead to mutation in repressor gene product which will result in constitutive expression of SOS genes like uvrA

3. mutation in uvrA operator will result in no binding of repressor to the operator nad will result in constitutive expression of uvrA

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