SUPPRESSION OF RECJ MUTATIONS OF ESCHERICHIA-COLI BY MUTATIONS IN TRANSLATION INITIATION FACTOR-IF3

We have isolated genetic suppressors of mutations in the recJ gene of Escherichia coli in a locus we term srjA. These srjA mutations cause p artial to complete alleviation of the recombination and UV repair defe cts conferred by recJ153 and recJ154 mutations in a recBC sbcA genetic background. The srjA gene was mapped to 37.5 min on the E. coli chrom osome. This chromosomal region from the srjA5 strain was cloned into a plasmid vector and was shown to confer recj suppression in a dominant fashion. Mutational analysis of this plasmid mapped srjA to the infC gene encoding translation initiation factor 3 (IF3). Sequence analysis revealed that all three srjA alleles cause amino acid substitutions o f IF3. Suppression of recj was shown to be allele specific: recJ153 an d recJ154 mutations were suppressible, but recJ77 and the insertion al lele recJ284=Tn10 were not. In addition, growth medium-conditional let hality was observed for strains carrying srjA mutations with the nonsu ppressible recj alleles. When introduced into recJ+ strains, srjA muta tions conferred hyperrecombinational and hyper-UV(r) phenotypes. An in teresting implication of these genetic properties of srjA suppression is that IF3 may regulate the expression of recj and perhaps other reco mbination genes and hence may regulate the recombinational capacity of the cell.