Topoisomerase Eucaryotic

Although the DNA-binding properties of several procaryotic topoisomerases have been well characterized, little information is currently available concerning eucaryotic enzymes. Some eucaryotic topoisomerases may be intimately associated with other nuclear proteins HeLa topoisomerases I and II have been found to be associated with chromatin (Javaherian and Liu, 1983 Liu et al., 1983b). HeLa topoisomerase I has been shown to bind to the nonhistone protein HMG17, which also stimulates DNA catenation by the enzyme (Javaherian and Liu, 1983 Tse et al., 1984). It has been suggested that type II topoisomerase is an important component of the chromosomal scaffold in interphase nuclei and mitotic chromosomes from chicken cell lines (Earnshaw et al., 1985). In addition, an ATP-dependent topoisomerase has been found associated with several other enzymes of DNA metabolism in a complex (termed the replitase complex) isolated from the nuclei of Chinese hamster embryo fibroblast cells (Noguchi et al., 1983). 

The interaction of eucaryotic type I topoisomerases with DNA can also be interrupted by alkali, leading to DNA cleavage (Champoux,... 

The cellular functions of topoisomerases demand much more attention, particularly in higher eucaryotes where little is known about their biological role. Tantalizing clues have come from their proposed involvement in chromosome structure and transcription complexes, and from demonstrations that their activities can be modulated by covalent modification. These aspects remain to be fully explored. 

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