EXPRESSION OF THE RECA GENE IN RECOMBINATION-DEFICIENT (REC-) STRAINS OF ESCHERICHIA-COLI

Basal and induced levels of recA expression in wild-type and isogenic derivatives of Escherichia coli carrying various rec mutations were measured using a low-copy number recA(po)-lacZ fusion, pKLC3.2. Basal recA expression in wild-type and isogenic derivatives containing single rec- mutations, as well as in the recBCsbcA strain and isogenic recA, recF and recJ derivatives, ranged from 1000 to 3900 units. In the recBCsbcBC strain and isogenic recL and recN derivatives basal recA expressions were 3- to 5-fold higher than that of wild-type cells and were inducible by mitomycin C. Except for the recA and lexA3(lnd-) mutants, recA expression was induced by mitomycin C in wild-type cells and its isogenic recB, recD, recF, recG, recJ, recL, recN, recO and ruv derivatives. RecF was required for induction of recA expression by mitomycin C, but not by naladixic acid in the recBCsbcA and recBCsbcBC genetic backgrounds. In wild-type cells, induction of recA expression by naladixic acid required the recBC, but not the recD function of the RecBCD enzyme. This requirement is suppressed by either an additional sbcA or sbcC mutation, but not by an sbcB mutation.