recA operator mutations and their usefulness.

Mutations at three positions in the operator for recA have been detected, cloned and sequenced. Derepressed amounts of recA protein vary over a forty-fold range and correlate well with reduced affinities for lexA repressor of the mutant operators. One mutant confirms the region of major groove interaction between repressor and operator. Another has been used to demonstrate that RecF pathway genes other than recA are under lexA control.