Replication fork assembly at recombination intermediates is required for bacterial growth

PriA, a 3' --> 5' DNA helicase, directs assembly of a primosome on some bac teriophage and plasmid DNAs, Primosomes are multienzyme replication machine s that contribute both the DNA-unwinding and Oliazaki fragment-priming func tions at the replication fork. The role of PriA in chromosomal replication is unclear. The phenotypes of priA null mutations suggest that the protein participates in replication restart at recombination intermediates. We show here that PriA promotes replication fork assembly at a D loop, an intermed iate formed during initiation of homologous recombination. We also show tha t DnaC810, encoded by a naturally arising intergenic suppressor allele of t he priA2::kan mutation, bypasses the need for PriA during replication fork assembly at D loops in vitro. These findings underscore the essentiality of replication fork restart at recombination intermediates under normal growt h conditions in bacteria.