title: E. coli DNA replication in the absence of free β clamps.
abstract: During DNA replication, repetitive synthesis of discrete Okazaki fragments requires mechanisms that guarantee DNA polymerase, clamp, and primase proteins are present for every cycle. In Escherichia coli, this process proceeds through transfer of the lagging-strand polymerase from the β sliding clamp left at a completed Okazaki fragment to a clamp assembled on a new RNA primer. These lagging-strand clamps are thought to be bound by the replisome from solution and loaded a new for every fragment. Here, we discuss a surprising, alternative lagging-strand synthesis mechanism: efficient replication in the absence of any clamps other than those assembled with the replisome. Using single-molecule experiments, we show that replication complexes pre-assembled on DNA support synthesis of multiple Okazaki fragments in the absence of excess β clamps. The processivity of these replisomes, but not the number of synthesized Okazaki fragments, is dependent on the frequency of RNA-primer synthesis. These results broaden our understanding of lagging-strand synthesis and emphasize the stability of the replisome to continue synthesis without new clamps.
authors: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.
authors: Nathan A
authors: NA
authors: Tanner
authors: Gökhan
authors: G
authors: Tolun
authors: Joseph J
authors: JJ
authors: Loparo
authors: Slobodan
authors: S
authors: Jergic
authors: Jack D
authors: JD
authors: Griffith
authors: Nicholas E
authors: NE
authors: Dixon
authors: Antoine M
authors: AM
authors: van Oijen
mesh_terms: D004247:DNA / Q000096:biosynthesis*; D004258:DNA Polymerase III / Q000172:deficiency*; D004261:DNA Replication / Q000502:physiology*; D004926:Escherichia coli / Q000502:physiology*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008954:Models, Biological
chemical_list: C022262:Okazaki fragments; D004247:DNA; C101139:beta subunit, DNA polymerase III; D004258:DNA Polymerase III