title: Interaction of the sliding clamp beta-subunit and Hda, a DnaA-related protein.
abstract: In Escherichia coli, interactions between the replication initiation protein DnaA, the beta subunit of DNA polymerase III (the sliding clamp protein), and Hda, the recently identified DnaA-related protein, are required to convert the active ATP-bound form of DnaA to an inactive ADP-bound form through the accelerated hydrolysis of ATP. This rapid hydrolysis of ATP is proposed to be the main mechanism that blocks multiple initiations during cell cycle and acts as a molecular switch from initiation to replication. However, the biochemical mechanism for this crucial step in DNA synthesis has not been resolved. Using purified Hda and beta proteins in a plate binding assay and Ni-nitrilotriacetic acid pulldown analysis, we show for the first time that Hda directly interacts with beta in vitro. A new beta-binding motif, a hexapeptide with the consensus sequence QL[SP]LPL, related to the previously identified beta-binding pentapeptide motif (QL[SD]LF) was found in the amino terminus of the Hda protein. Mutants of Hda with amino acid changes in the hexapeptide motif are severely defective in their ability to bind beta. A 10-amino-acid peptide containing the E. coli Hda beta-binding motif was shown to compete with Hda for binding to beta in an Hda-beta interaction assay. These results establish that the interaction of Hda with beta is mediated through the hexapeptide sequence. We propose that this interaction may be crucial to the events that lead to the inactivation of DnaA and the prevention of excess initiation of rounds of replication.
authors.affiliation: CSIRO Livestock Industries, Queensland Bioscience Precinct, St. Lucia Queensland Dominion 4067, Australia.
authors.forename: Mareike
authors.initials: M
authors.lastname: Kurz
authors.forename: Brian
authors.initials: B
authors.lastname: Dalrymple
authors.forename: Gene
authors.initials: G
authors.lastname: Wijffels
authors.forename: Kritaya
authors.initials: K
authors.lastname: Kongsuwan
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000502:physiology; D020816:Amino Acid Motifs; D001665:Binding Sites; D004258:DNA Polymerase III / Q000737:chemistry* / Q000502:physiology; D004261:DNA Replication; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000502:physiology
chemical_list: D029968:Escherichia coli Proteins; C101139:beta subunit, DNA polymerase III; D004258:DNA Polymerase III; D000251:Adenosine Triphosphatases; C435211:Hda protein, E coli