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[摘要]：DNA topoisomerases play critical roles in regulating DNA topology and are essential enzymes for cell survival. In this study, a gene encoding type IA DNA topoisomerase was cloned from Staphylococcus aureus (S. aureus) sp. strain C-66, and the biochemical properties of recombinant enzyme was characterized. The nucleotide sequence analysis showed that the cloned gene contained an open reading frame (2070 bp) that could encode a polypeptide of 689 amino acids. The cloned gene actually produced 79.1 kDa functional enzyme (named Sau-Topol) in Escherichia coli (E. coil). Sau-Topol enzyme purified from E. coli showed ATP-independent and Mg2+-dependent manners for relaxing negatively supercoiled DNA. The relaxation activity of Sau-Topol was inhibited by camptothecin, but not by nalidixic acid and etoposide. Cleavage site mapping showed that the enzyme could preferentially bind to and cleave the sequence GGNN down arrow CAT (N and down arrow represent any nucleotide and cleavage site, respectively). All these results suggest that the purified enzyme is type IA DNA topoisomerase. In addition, domain mapping analysis showed that the enzyme was composed of conserved four domains (I through IV), together with a variable C-terminal region containing a unique domain (C). 2011 Elsevier Inc. All rights reserved. |
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