Purification and nuclear localization of a type I topoisomerase from Crithidia fasciculata.

A type I topoisomerase has been purified to near homogeneity from the trypanosomatid Crithidia fasciculata. The topoisomerase consists of a single 79 kDa polypeptide. The enzyme does not require divalent cations but is stimulated 10-20 fold by the presence of MgCl2. ATP does not affect enzyme activity, while Berenil, N-ethylmaleimide and ethidium bromide are inhibitory. Immunoblots show that the 79 kDa polypeptide is the most prevalent form of the enzyme in extracts of freshly lysed cells and is immunogenically conserved among a variety of trypanosomes. The topoisomerase was localized to the cell nucleus by double antibody immunofluorescence.