Suppose a researcher is designing a set of mutations in the SOS response genes i

Question

Suppose a researcher is designing a set of mutations in the SOS response genes in E. coli that she hopes will prevent induction of the SOS response by LexA and RecA. What types of mutations would result in continual repression of SOS genes by LexA? Choose ALL that apply.

A. A mutation that increases the binding affinity of RecA for LexA.

B. Mutations that allow LexA to undergo autocatalytic cleavage without RecA binding.

C. Mutations to LexA structure that prevent RecA binding to LexA.

D. Amino acid substitutions that inactivate the LexA active site.

E. A mutation that prevents RecA binding to single-stranded DNA.

Explanation / Answer

Explanation

SOS response is a coordinated cellular response in E.coli, it is activated only when the bacterial chromosome is extensively damaged and promotes the survival of organism by affecting the expression of proteins that are involved in cell division, replication, recombination and excision repair.

The basic mechanism of regulation is very simple. The important regulatory protein are a repressor, called LexA repressor and a RecA protein.

NOTE: LexA repressor normally synthesized as a dimer of Repressor and Activator subunits, autocatalytic cleavage of lexA repressor would results in release of activator domain and this domain further activates the transcription of SOS genes.

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