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.