title: Biochemical properties of a plastidial DNA polymerase of rice.
abstract: Plastids are organelles unique to plant cells and are responsible for photosynthesis and other metabolic functions. Despite their important cellular roles, relatively little is known about the mechanism of plastidial DNA replication and repair. Recently, we identified a novel DNA polymerase in Oryza Sativa L. (OsPOLP1, formerly termed OsPolI-like) that is homologous to prokaryotic DNA polymerase Is (PolIs), and suggested that this polymerase might be involved in plastidial DNA replication and repair. Here, we propose to rename the plant PolI homologs as DNA polymerase pi (POLP), and investigate the biochemical properties of full-length OsPOLP1. The purified OsPOLP1 elongated both DNA and RNA primer hybridized to a DNA template, and possessed a 3' exonuclease activity. Moreover, OsPOLP1 displayed high processivity and fidelity, indicating that this polymerase has the biochemical characteristics appropriate for DNA replication. We found that POLPs have two extra sequences in the polymerase domain that are absent in prokaryotic PolIs. Deletion of either insert from OsPOLP1 caused a decrease in DNA synthetic activity, processivity, and DNA binding activity. In addition, OsPOLP1 efficiently catalyzed strand displacement on nicked DNA with a 5'-deoxyribose phosphate, suggesting that this enzyme might be involved in a repair pathway similar to long-patch base excision repair. These results provide insights into the possible role of POLPs in plastidial DNA replication and repair.
authors.affiliation: Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba-ken, 278-8510, Japan. j6498055@yahoo.co.jp
authors.forename: Ryo
authors.initials: R
authors.lastname: Takeuchi
authors.forename: Seisuke
authors.initials: S
authors.lastname: Kimura
authors.forename: Ai
authors.initials: A
authors.lastname: Saotome
authors.forename: Kengo
authors.initials: K
authors.lastname: Sakaguchi
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D017931:DNA Primers; D004260:DNA Repair; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000201:enzymology*; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D004259:DNA-Directed DNA Polymerase