title: The carboxyl-terminal residues of Escherichia coli DNA topoisomerase III are involved in substrate binding.
abstract: The nucleic acid-binding domain of Escherichia coli DNA topoisomerase III (Topo III) has been identified using a selection procedure designed to isolate inactive Topo III polypeptides. Deletion of this binding domain, contained in the carboxyl terminus of Topo III, results in a drastic reduction in the ability of the enzyme to bind to single-stranded DNA and RNA substrates. Successive truncation of the enzyme within this region results in the gradual loss of nucleic acid binding activity and in a gradual change in the mechanism of Topo III-catalyzed relaxation of negatively supercoiled DNA. The reduction of nucleic acid binding activity of the truncated polypeptides does not result in a loss of cleavage site specificity for the enzyme, suggesting that other amino acids are involved in the positioning of the nucleic acid within the nicking/closing site of the topoisomerase.
authors.affiliation: Molecular and Cell Biology Program, University of Maryland at Baltimore 21201.
authors.forename: H L
authors.initials: HL
authors.lastname: Zhang
authors.forename: R J
authors.initials: RJ
authors.lastname: DiGate
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D004264:DNA Topoisomerases, Type I / Q000737:chemistry* / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D004278:DNA, Superhelical / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D009838:Oligodeoxyribonucleotides; D016601:RNA-Binding Proteins; D012313:RNA; D004264:DNA Topoisomerases, Type I