PMID:11589970

Citation	Roche, CJ and Tse-Dinh, YC (2001) Effect of phosphorothioate substitutions on DNA cleavage by Escherichia coli DNA topoisomerase I. Int. J. Biol. Macromol. 29:175-80
Abstract	To evaluate the structural influence of the DNA phosphate backbone on the activity of Escherichia coli DNA topoisomerase I, modified forms of oligonucleotide dA(7) were synthesized with a chiral phosphorothioate replacing the non-bridging oxygens at each position along the backbone. A deoxy-iodo-uracil replaced the 5'-base to crosslink the oligonucleotides by ultraviolet (UV) and assess binding affinity. At the scissile phosphate there was little effect on the cleavage rate. At the +1 phosphate, the rectus phosphorus (Rp)-thio-substitution reduced the rate of cleavage by a factor of 10. At the +3 and -2 positions from the scissile bond, the Rp-isomer was cleaved at a faster rate than the sinister phosphorus (Sp)-isomer. The results demonstrate the importance of backbone contacts between DNA substrate and E. coli topoisomerase I.
Links	PubMed
Keywords	Binding Sites; Catalytic Domain; DNA/chemistry; DNA/metabolism; DNA Topoisomerases, Type I/metabolism; Dose-Response Relationship, Drug; Escherichia coli/enzymology; Models, Chemical; Oligonucleotides/chemistry; Oxygen/metabolism; Phosphates/chemistry; Protein Binding; Time Factors
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