The SOS Regulatory System is Activated By

Question

The SOS regulatory system is activated by
A) the activity of DNA polymerase IV.
B) DNA damage.
C) transcription of LexA.
D) repression of RecA.

Accepted Answer

The SOS regulatory system is activated by DNA damage. When there is significant DNA damage, the RecA protein binds to single-stranded DNA at the site of damage, leading to the self-cleavage of LexA protein repressor, resulting in the derepression of SOS genes. This leads to the induction of DNA repair and mutagenesis pathways. DNA polymerase IV is a part of the SOS response and is induced following induction of the SOS genes. Repression of RecA would not activate the system and transcription of LexA would occur after activation, not before, making choice B the only correct option.