title: The ATP-operated clamp of human DNA topoisomerase IIalpha: hyperstimulation of ATPase by "piggy-back" binding.
abstract: We have constructed a series of clones encoding N-terminal fragments of human DNA topoisomerase IIalpha. All fragments exhibit DNA-dependent ATPase activity. Fragment 1-420 shows hyperbolic dependence of ATPase on DNA concentration, whereas fragment 1-453 shows hyperstimulation at low ratios of DNA to enzyme, a phenomenon found previously with the full-length enzyme. The minimum length of DNA found to stimulate the ATPase activity was approximately 10 bp; fragments >or=32 bp manifest the hyperstimulation phenomenon. Molecular mass studies show that fragment 1-453 is a monomer in the absence of nucleotides and a dimer in the presence of nucleotide triphosphate. The results are consistent with the role of the N-terminal domain of topoisomerase II as an ATP-operated clamp that dimerises in the presence of ATP. The hyperstimulation effect can be interpreted in terms of a "piggy-back binding" model for protein-DNA interaction.
authors.affiliation: Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK.
authors.forename: Spencer
authors.initials: S
authors.lastname: Campbell
authors.forename: Anthony
authors.initials: A
authors.lastname: Maxwell
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents / Q000494:pharmacology; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000737:chemistry* / Q000378:metabolism*; D004268:DNA-Binding Proteins; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008954:Models, Biological; D008969:Molecular Sequence Data; D010957:Plasmids; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D008024:Ligands; D011506:Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; D004250:DNA Topoisomerases, Type II