title: Deletions at the carboxyl terminus of vaccinia DNA topoisomerase affect DNA binding and enhance distributivity in DNA relaxation.
abstract: Vaccinia topoisomerase relaxes DNA through the formation of a covalent DNA-(3'-phosphotyrosyl)protein intermediate at sites containing the sequence 5'-(T/C)CCTT/. The active site, Tyr-274, is situated near the carboxyl terminus of the 314 amino acid enzyme. Here, we report the effects of serial C-terminal deletions. Removal of five amino acids had no effect on topoisomerase activity. However, deletion of 10, 15, or 20 amino acids rendered the enzyme distributive in DNA relaxation, incrementally slowed the rate of single-turnover DNA cleavage, and progressively diminished DNA binding affinity, without altering the sequence specificity of DNA cleavage. These effects lead us to speculate that the region downstream of the active site, which is not well-conserved among the poxvirus-encoded topoisomerases, is a component of the proposed circumferential interface between the enzyme and duplex DNA.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA.
authors.forename: L K
authors.initials: LK
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Shuman
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009690:Nucleic Acid Conformation; D017384:Sequence Deletion; D012965:Sodium Chloride / Q000494:pharmacology; D013379:Substrate Specificity; D014616:Vaccinia virus / Q000201:enzymology*
chemical_list: D004268:DNA-Binding Proteins; D012965:Sodium Chloride; D004247:DNA; D004264:DNA Topoisomerases, Type I; D008274:Magnesium