19 DNA Gyrase and Other Type II Topoisomerases
1981; Elsevier BV; Linguagem: Inglês
10.1016/s1874-6047(08)60345-5
ISSN1874-6047
Autores Tópico(s)Gyrotron and Vacuum Electronics Research
ResumoDNA topoisomerases are enzymes that catalyze changes in the topological structure of DNA molecules. The basic chemical reaction carried out by topoisomerases is a cycle of breakage and rejoining of DNA chains, in the course of which the phosphodiester bond energy is conserved by the formation of a covalent enzyme–DNA intermediate. There are two classes of topoisomerases—namely, (1) DNA topoisomerase I or ω protein and (2) type II topoisomerases. This chapter focuses on type II topoisomerases. Their basic mode of operation involves the generation of transient double-strand breaks in DNA. Among type II enzymes, two subclasses are distinguished. DNA gyrases primarily catalyze the conversion of relaxed DNA to a superhelical form, thus transforming the DNA structure to one of higher free energy at the expense of ATP hydrolysis. Other type II topoisomerases stimulate the reverse reaction, converting supercoiled DNA to more relaxed forms. DNA gyrase has been isolated only from prokaryotic sources. The best-studied enzymes are those from Escherichia coli and Micrococcus luteus. DNA gyrase can be used to prepare negatively and positively supercoiled DNA. All type II topoisomerases can be used to resolve knotted and catenated structures without permanently breaking the DNA.
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