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Nucleic Acids Research, 1983, Vol. 11, No. 9 2779-2800
© 1983

ENZYMOLOGY

Biochemical characterization of topoisomerase I purified from avian erythrocytes

Douglas K. Trask and Mark Twain Muller

Department of Microbiology, The Ohio State University Columbus, OH 43210, USA

Received October 19, 1982. Revised February 24, 1983. Accepted February 24, 1983.

A type I topoisomerase has been purified from avian erythrocyte nuclei. The most pure fraction contains one major polypeptide of Mr = 105,000 (80% of total) and several minor ones of lower molecular weight. Active forms of the topoisomerase were identified by covalently binding the enzyme to P-DNA, digesting with nuclease and detecting 32-p labeled peptides by sodium dodecyl sulfate polyaorylamide gel electrophoresis. Topoisomerase activity, as measured by the ability to oovalently bind DMA, is associated with the following peptides: Mr = 105, 83, 54 and 30,000. The similar chromatographic properties of the various forms of topoisomerase suggests a common structural Identity as previously proposed for the HeLa topoisomerase I (Liu, L.F. and Miller, K.G. (1981) Proc. Nat 1. Acad. Soi. USA 78, 3487–3191). The avian enzyme is similar to other eucaryotic type I DNA topoisomerases in that it covalently binds double and single stranded DNA forming an enzyme linked to the 3'-phosphoryl end and after binding to single stranded DNA it can transfer the single stranded donor DNA to an acceptor DNA possessing 5'-OH end groups. The binding site size of topoisomerase on DNA has also been determined using micrococoal nuclease to digest unprotected DNA in the native enzyme/DNA complex. The enzyme blocks access to the helix over a span of 25 bp. These findings are discussed in light of the distribution and function of topoisomerase I in chromatin.


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