title: Mammalian topoisomerase I has base mismatch nicking activity.
abstract: The all-type nicking enzyme (ATE) from human HeLa cells or calf thymus can nick DNA at the first phosphodiester bond 5' to all 8 possible mismatched bases. The strand disparity of this nicking is influenced by the neighboring nucleotide sequences. After nicking, the ATE covalently binds to the 3' end of the DNA product to form a cleavable complex, whose formation is insensitive to camptothecin, a specific inhibitor of eukaryotic topoisomerase I (Topo-I). During the purification of ATE from calf thymus, a Mg(2+)-independent relaxation activity, characteristic of eukaryotic Topo-I, copurifies with the mismatch-nicking activity. The ATE from calf thymus may be a breakdown product of Topo-I. N-terminal amino acid analysis indicates that one of the polypeptides with ATE activity contains the C-terminal portion of Topo-I. Moreover, active human Topo-I, expressed as a fusion protein in Escherichia coli, is also capable of nicking all 8 base mispairs in the absence of Mg2+. This mismatch-specific nicking activity may be a novel property of the mammalian Topo-I.
authors.affiliation: Department of Biological Chemistry, University of Maryland, School of Medicine, Baltimore 21201.
authors.forename: Y C
authors.initials: YC
authors.lastname: Yeh
authors.forename: H F
authors.initials: HF
authors.lastname: Liu
authors.forename: C A
authors.initials: CA
authors.lastname: Ellis
authors.forename: A L
authors.initials: AL
authors.lastname: Lu
mesh_terms: D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D002166:Camptothecin / Q000494:pharmacology; D002417:Cattle; D002845:Chromatography; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D017931:DNA Primers; D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D017886:Durapatite; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D015183:Restriction Mapping; D013379:Substrate Specificity; D013950:Thymus Gland / Q000201:enzymology*
chemical_list: D017931:DNA Primers; D009838:Oligodeoxyribonucleotides; D011993:Recombinant Fusion Proteins; D004247:DNA; D017886:Durapatite; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin