Escherichia coli and Bacillus subtilis PriA proteins essential for recombination-dependent DNA replication: Involvement of ATPase/helicase activity of PriA for inducible stable DNA replication

Abstract

The E. coli PriA protein, a DEXH-type DNA helicase with unique zinc finger-like motifs interrupting the helicase domains, is an essential component of the φX174-type primosome and plays critical roles in RecA-dependent inducible and constitutive stable DNA replication (iSDR and cSDR, respectively) as well as in recombination-dependent repair of double-stranded DNA breaks. B. subtilis PriA (BsPriA) protein contains the conserved helicase domains as well as zinc finger-like motifs with 34% overall identity with the E. coli counterpart. We overexpressed and purified BsPriA and examined its biochemical properties. BsPriA binds specifically to both n'- pas (primosome assembly site) and D-loop and hydrolyzes ATP in the presence of n'- pas albeit with a specific activity about 30% of that of E. coli PriA. However, it is not capable of supporting n'- pas-dependent replication in vitro, nor is it able to support ColE1-type plasmid replication in vivo which requires the function of the φX174-type primosome. We also show that a zinc finger mutant is not able to support recombination-dependent DNA replication, as measured by the level of iSDR after a period of thymine starvation, nor wild-type level of growth, cell morphology and UV resistance. Unexpectedly, we discovered that an ATPase-deficient mutant (K230D) is not able to support iSDR to a full extent, although it can restore normal growth rate and UV resistance as well as non-filamentous morphology in priA1::kan mutant. K230D was previously reported to be fully functional in assembly of the φX174-type primosome at a single-stranded n'- pas. Our results indicate that ATP hydrolysis/ helicase activity of PriA may be specifically required for DNA replication from recombination intermediates in vivo.