Suppression of the Defects in rdgB Mutants of Escherichia coli K-12 by the Cloned purA Gene

A gene suppressing the defects of Escherichia coli rdgB (recA-dependent growth) and recA(Ts) rdgB mutants was cloned. The cloned gene suppresses the hyper-Rec phenotype and the enhanced level of SOS functions in rdgB mutants at the nonpermissive temperature. We identified the cloned gene as purA. An rdgB mutant was initially characterized as having a mutation that made the cell dependent on recA+ for growth (1). The properties of rdgB and rdgB recA(Ts) mutants suggest a role for the rdgB gene product in maintaining the structural integrity of the chromosome. Although rdgB mu-tants grow normally, they are hyper-recombinogenic and partially induced for the SOS response. The rdgB recA(Ts) double mutant rapidly loses viability after a shift to restric-tive temperature owing to induction of a high level of endogenous DNA damage. We previously described the isolation of recombinant plasmids carrying inserts derived from Escherichia coli chromosomal DNA which comple