Practice question

Severe DNA damage causes accumulation of single-stranded DNA activating RecA to stimulate autocleavage of LexA repressor derepressing over 40 SOS genes regulon. Among strongly induced are umuD and umuC genes encoding Pol V, Y-family error-prone polymerase capable of copying past pyrimidine dimers that block Pol III. Pol V requires RecA nucleoprotein filament for activation as mutasome complex. Its expression relatively late in SOS response provides last-resort translesion synthesis when excision repair incomplete enabling survival despite persisting lesions but dramatically increasing mutation rate.