Developmental And Functional Regulation Of DNA Topoisomerase II in Postnatal Rat Testis

Abstract

Characterization of the polyoma virus chromosome as a circular, double-stranded, supercoiled DNA (Weil and Vinograd, 1963; Vinograd et al.,-1965) made it apparent that the DNA enzymatic machinery faces a formidable problem in ensuring faithful replication of genetic material. These studies initiated a search for enzymatic activities that are capable of overcoming this topological barrier and led to the discovery of DNA topoisomerase I, originally denoted as omega protein (Wang, 1971), followed by DNA gyrase (Gellert et al., 1976) from Escherichia coli. It is now established that Escherichia coli encodes four distinct topoisornerases. These include topoisomerase I (topA) (Wang, 1971), topoisomerase II (gyrA and gyrB) (Gellert et al., 1976), topoisomerase III (topB) (DiGate and Marians, 1988) and topoisomerase IV (parC and parE) (Kato et al, 1990; 1992). These enzymes perform various non-overlapping functions in vivo (reviewed in Roca, 1995). Additionally, a 'reverse gyrase", capable of introducing positive supercoils into DNA, in an ATP dependent manner, has been characterized from hyperthermophiles (Kikuchi and Asai, 1984; Kozyavkin et al., 1994).