The Cleavage of DNA by Type-I DNA Topoisomerases
This extract was created in the absence of an abstract.
Excerpt
DNA topoisomerases are ubiquitous enzymes that catalyze the transient breakage of DNA backbone bonds and the passage of DNA strands through these transient enzyme-operated DNA gates (for reviews, see Champoux 1978; Wang and Liu 1979; Cozzarelli 1980; Gellert 1981a,b; Wang 1981, 1982a,b). Two mechanistically distinct classes of topoisomerases are known: (1) the type-I enzymes catalyze the breakage and rejoining of DNA strands one at a time and (2) the type-II enzymes catalyze the breakage and rejoining of both strands of double-stranded DNA in concert. The type-I enzymes require no energy cofactors such as ATP or NAD, whereas all known type-II enzymes are strongly ATP dependent.
In a topoisomerase-catalyzed breakage and rejoining of a DNA backbone bond, the same bond that is broken is rejoined. Thus, the action of a topoisomerase is usually manifested by a change in the topological state of a circular DNA substrate, hence its name (Wang and...
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↵* Present address: Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02139.
