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Mechanistic Aspects of DNA Topoisomerases

1986; Academic Press; Linguagem: Inglês

10.1016/s0065-3233(08)60526-4

1557-8941

Anthony Maxwell, Martin Gellert,

Bioactive Compounds and Antitumor Agents

Publisher Summary Topoisomerases are a diverse and important group of enzymes. Although attention has until recently been focused on their ability to interconvert DNA topoisomers, this does not necessarily constitute the primary biological function for all of them. DNA topoisomerases are enzymes that catalyze changes in the topology of circular DNA. With a closed-circular double-stranded DNA, one type of reaction alters the number of times the two strands are wound around each other and thus changes the degree of supercoiling. Supercoiled DNA molecules are prevalent in cells, and enzymes that can modify this property are important in DNA metabolism. Reactions involving other topological isomers of DNA are also known; various topoisomerases can form or resolve knotted or catenated structures in circular duplex DNA, or form knots in single-stranded circular DNA. Some of these reactions also have biological importance; for instance, replication of a circular-duplex DNA often produces two catenated circles, which then have to be separated. Cells of all organisms examined to date have been found to contain DNA topoisomerases; commonly there are several distinct types in a cell. Where a genetic test has been feasible, the presence of at least one topoisomerase has been found to be essential for cell growth. This chapter discusses various lines of information bearing on the enzymatic mechanisms of topoisomerases.