The ATP-operated clamp of human DNA topoisomerase IIalpha: hyperstimulation of ATPase by "piggy-back" binding |
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Authors: | Campbell Spencer Maxwell Anthony |
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Affiliation: | Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK. |
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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. |
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Keywords: | DNA gyrase supercoiling anti-tumour drugs DNA-protein interactions |
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