Replication mutations differentially enhance RecA-dependent and RecA-independent recombination between tandem repeats in Bacillus subtilis

We have studied DNA recombination between 513 bp tandem direct repeats pres ent in a kanamycin resistance gene inserted in the Bacillus subtilis chromo some. Tandem repeat deletion was not significantly affected by a recA mutat ion. However, recombination was stimulated by mutations in genes encoding r eplication proteins, including the primosomal proteins DnaB, DnaD and the D naG primase, the putative DNA polymerase III subunits PolC, DnaN and DnaX, as well as the DNA polymerase DnaE. Hyper-recombination was found to be dep endent on RecA in the dnaE, dnaN and dnaX mutants, whereas the dnaG and dna D mutants stimulated recombination independently of RecA. Altogether, these data show that both RecA-dependent and RecA-independent mechanisms contrib ute to recombination between tandem repeats in B. subtilis and that both ty pes of recombination are stimulated by replication mutations.