title: Escherichia coli PriA helicase: fork binding orients the helicase to unwind the lagging strand side of arrested replication forks.
abstract: Escherichia coli PriA is a primosome assembly protein with 3' to 5' helicase activity whose apparent function is to promote resumption of DNA synthesis following replication-fork arrest. Here, we describe how initiation of helicase activity on DNA forks is influenced by both fork structure and by single-strand DNA-binding protein. PriA could recognize and unwind forked substrates where one or both arms were primarily duplex, and PriA required a small (two bases or larger) single-stranded gap at the fork in order to initiate unwinding. The helicase was most active on substrates with a duplex lagging-strand arm and a single-stranded leading-strand arm. On this substrate, PriA was capable of translocating on either the leading or lagging strands to unwind the duplex ahead of the fork or the lagging-strand duplex, respectively. Fork-specific binding apparently orients the helicase domain to unwind the lagging-strand duplex. Binding of single-strand-binding protein to forked templates could inhibit unwinding of the duplex ahead of the fork but not unwinding of the lagging-strand duplex or translocation on the lagging-strand template. While single-strand-binding protein could inhibit binding of PriA to the minimal, unforked DNA substrates, it could not inhibit PriA binding to forked substrates. In the cell, single-strand-binding protein and fork structure may direct PriA helicase to translocate along the lagging-strand template of forked structures such that the primosome is specifically assembled on that DNA strand.
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, 3900 Reservoir Road NW, Washington, DC 20007, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Jones
authors.forename: H
authors.initials: H
authors.lastname: Nakai
mesh_terms: D001483:Base Sequence; D004265:DNA Helicases / Q000378:metabolism*; D017931:DNA Primers; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D051716:Replication Protein A; D013379:Substrate Specificity; D013698:Templates, Genetic
chemical_list: D017931:DNA Primers; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D051716:Replication Protein A; D004265:DNA Helicases