title: The G157C mutation in the Escherichia coli sliding clamp specifically affects initiation of replication.
abstract: Escherichia coli cells with a point mutation in the dnaN gene causing the amino acid change Gly157 to Cys, were found to underinitiate replication and grow with a reduced origin and DNA concentration. The mutant β clamp also caused excessive conversion of ATP-DnaA to ADP-DnaA. The DnaA protein was, however, not the element limiting initiation of replication. Overproduction of DnaA protein, which in wild-type cells leads to over-replication, had no effect in the dnaN(G157C) mutant. Origins already opened by DnaA seemed to remain open for a prolonged period, with a stage of initiation involving β clamp loading, presumably limiting the initiation process. The existence of opened origins led to a moderate SOS response. Lagging strand synthesis, which also requires loading of the β clamp, was apparently unaffected. The result indicates that some aspects of β clamp activity are specific to the origin. It is possible that the origin specific activities of β contribute to regulation of initiation frequency.
authors.affiliation: Department of Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway.
authors.forename: Line
authors.initials: L
authors.lastname: Johnsen
authors.forename: Ingvild
authors.initials: I
authors.lastname: Flåtten
authors.lastname: Morigen
authors.forename: Bjørn
authors.initials: B
authors.lastname: Dalhus
authors.forename: Magnar
authors.initials: M
authors.lastname: Bjørås
authors.forename: Torsten
authors.initials: T
authors.lastname: Waldminghaus
authors.forename: Kirsten
authors.initials: K
authors.lastname: Skarstad
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D019943:Amino Acid Substitution / Q000235:genetics*; D001426:Bacterial Proteins / Q000378:metabolism; D004258:DNA Polymerase III / Q000378:metabolism*; D004261:DNA Replication; D004269:DNA, Bacterial / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D020125:Mutation, Missense
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D000255:Adenosine Triphosphate; C101139:beta subunit, DNA polymerase III; D004258:DNA Polymerase III