title: Comparison of the kinetic parameters of the truncated catalytic subunit and holoenzyme of human DNA polymerase ɛ.
abstract: Numerous genetic studies have provided compelling evidence to establish DNA polymerase ɛ (Polɛ) as the primary DNA polymerase responsible for leading strand synthesis during eukaryotic nuclear genome replication. Polɛ is a heterotetramer consisting of a large catalytic subunit that contains the conserved polymerase core domain as well as a 3'→5' exonuclease domain common to many replicative polymerases. In addition, Polɛ possesses three small subunits that lack a known catalytic activity but associate with components involved in a variety of DNA replication and maintenance processes. Previous enzymatic characterization of the Polɛ heterotetramer from budding yeast suggested that the small subunits slightly enhance DNA synthesis by Polɛ in vitro. However, similar studies of the human Polɛ heterotetramer (hPolɛ) have been limited by the difficulty of obtaining hPolɛ in quantities suitable for thorough investigation of its catalytic activity. Utilization of a baculovirus expression system for overexpression and purification of hPolɛ from insect host cells has allowed for isolation of greater amounts of active hPolɛ, thus enabling a more detailed kinetic comparison between hPolɛ and an active N-terminal fragment of the hPolɛ catalytic subunit (p261N), which is readily overexpressed in Escherichia coli. Here, we report the first pre-steady-state studies of fully-assembled hPolɛ. We observe that the small subunits increase DNA binding by hPolɛ relative to p261N, but do not increase processivity during DNA synthesis on a single-stranded M13 template. Interestingly, the 3'→5' exonuclease activity of hPolɛ is reduced relative to p261N on matched and mismatched DNA substrates, indicating that the presence of the small subunits may regulate the proofreading activity of hPolɛ and sway hPolɛ toward DNA synthesis rather than proofreading.
authors: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA.
authors: Walter J
authors: WJ
authors: Zahurancik
authors: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA.
authors: Andrey G
authors: AG
authors: Baranovskiy
authors: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA.
authors: Tahir H
authors: TH
authors: Tahirov
authors: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA. Electronic address: suo.3@osu.edu.
authors: Zucai
authors: Z
authors: Suo
mesh_terms: D004247:DNA / Q000378:metabolism; D004257:DNA Polymerase II / Q000378:metabolism*; D004261:DNA Replication; D020035:Holoenzymes / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D000075223:Poly-ADP-Ribose Binding Proteins
chemical_list: D020035:Holoenzymes; D000075223:Poly-ADP-Ribose Binding Proteins; D004247:DNA; D004257:DNA Polymerase II; C119525:POLE protein, human
keywords: 3′→5′ exonuclease activity; DNA polymerase epsilon; Human DNA replication; Leading strand replication; Pre-steady-state kinetics