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Characterization of an altered DNA catalysis of a camptothecin-resistant eukaryotic topoisomerase I. 总被引:1,自引:0,他引:1 下载免费PDF全文
I I Gromova E Kjeldsen J Q Svejstrup J Alsner K Christiansen O Westergaard 《Nucleic acids research》1993,21(3):593-600
We investigated topoisomerase I activity at a specific camptothecin-enhanced cleavage site by use of a partly double-stranded DNA substrate. The cleavage site belongs to a group of DNA topoisomerase I sites which is only efficiently cleaved by wild-type topoisomerase I (topo I-wt) in the presence of camptothecin. With a mutated camptothecin-resistant form of topoisomerase I (topo I-K5) previous attempts to reveal cleavage activity at this site have failed. On this basis it was questioned whether the mutant enzyme has an altered DNA sequence recognition or a changed rate of catalysis at the site. Utilizing a newly developed assay system we demonstrate that topo I-K5 not only recognizes and binds to the strongly camptothecin-enhanced cleavage site but also has considerable cleavage/religation activity at this particular DNA site. Thus, topo I-K5 has a 10-fold higher rate of catalysis and a 10-fold higher affinity for DNA relative to topo I-wt. Our data indicate that the higher cleavage/religation activity of topo I-K5 is a result of improved DNA binding and a concomitant shift in the equilibrium between cleavage and religation towards the religation step. Thus, a recently identified point mutation which characterizes the camptothecin-resistant topo I-K5 has altered the enzymatic catalysis without disturbing the DNA sequence specificity of the enzyme. 相似文献
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Elongator complex: how many roles does it play? 总被引:2,自引:0,他引:2
Svejstrup JQ 《Current opinion in cell biology》2007,19(3):331-336
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