title: The predominant form of mammalian DNA topoisomerase I in vivo has a molecular mass of 100 kDa.
abstract: DNA topoisomerase I was purified to apparent homogeneity from human HeLa cells as a single polypeptide with a molecular mass of 100 kDa, as assayed by both gel filtration column chromatography and SDS-polyacrylamide gel electrophoresis. No smaller forms of the enzyme were detected in the purified fraction. Therefore, smaller forms, which have been observed by other investigators, are likely to be the result of proteolysis during isolation and are not relevant to the in vivo activity of DNA topoisomerase I.
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721.
authors.forename: D S
authors.initials: DS
authors.lastname: Samuels
authors.forename: N
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D016477:Artifacts; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification*; D006367:HeLa Cells / Q000201:enzymology; D006801:Humans; D008970:Molecular Weight
chemical_list: D004264:DNA Topoisomerases, Type I