title: DNA topoisomerase I cleavage sites in DNA and in nucleoprotein complexes.
abstract: The intracellular substrate for eukaryotic DNA topoisomerases is chromatin rather than protein-free DNA. Yet, little is known about the action of topoisomerases on chromatin-associated DNA. We have analyzed to what extent the organization of DNA in chromatin influences the accessibility of DNA molecules for topoisomerase I cleavage in vitro. Using potassium dodecyl sulfate precipitation (Trask et al., 1984), we found that DNA in chromatin is cleaved by the enzyme with somewhat reduced efficiency compared to protein-free DNA. Furthermore, using native SV40 chromatin and mononucleosomes assembled in vitro, we show that DNA bound to histone octamer complexes is cleaved by topoisomerase I and that the cleavage sites as well as their overall distribution are identical in histone-bound and in protein-free DNA molecules.
authors.affiliation: Division of Biology, University of Konstanz, FRG.
authors.forename: A
authors.initials: A
authors.lastname: Richter
authors.forename: J
authors.initials: J
authors.lastname: Ruff
mesh_terms: D001483:Base Sequence; D002384:Catalysis; D002843:Chromatin / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D004264:DNA Topoisomerases, Type I / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009698:Nucleoproteins / Q000737:chemistry / Q000235:genetics*; D009707:Nucleosomes / Q000737:chemistry; D013539:Simian virus 40; D013379:Substrate Specificity
chemical_list: D002843:Chromatin; D009698:Nucleoproteins; D009707:Nucleosomes; D004247:DNA; D004264:DNA Topoisomerases, Type I