DnaB, DnaD and DnaI proteins are components of the Bacillus subtilis replication restart primosome

Phenotypes of Bacillus subtilis priA mutants suggest that they are deficien t in the restart of stalled chromosomal replication forks. The presumed act ivity of PriA in the restart process is to promote the assembly of a multip rotein complex, the primosome, which functions to recruit the replication f ork helicase onto the DNA. We have proposed previously that three proteins involved in the initiation of replication at oriC in B. subtilis, DnaB, Dna D and Dnal, are components of the PriA primosome in this bacterium. However , the involvement of these proteins in replication restart has not yet been studied. Here, we describe dnaB mutations that suppress the phenotypes of B. subtilis priA mutants. In a representative mutant, the DnaC helicase is loaded onto single-stranded DNA in a PriA-independent, DnaD- and Dnal-depen dent manner. These observations confirm that DnaB, DnaD and Dnal are primos omal proteins in B. subtilis. Moreover, their involvement in the suppressio n of priA phenotypes shows that they participate in replication fork restar t in B. subtilis.