title: Identification of a DNA supercoiling activity in Saccharomyces cerevisiae.
abstract: A relaxed plasmid DNA is shown to become positively supercoiled in cell extracts from top1 strains of Saccharomyces cerevisiae. This positive supercoiling activity is dependent on the presence of bacterial DNA topoisomerase I and ATP (or dATP), and the positive supercoils generated in this reaction are not constrained by protein(s). Non-hydrolyzable ATP analogs cannot substitute for ATP in this supercoiling reaction, and the supercoiling activity is not due to RNA synthesis. The presence of an ARS sequence in the DNA does not alter the activity. Furthermore, this activity is equally active against UV irradiated or intact DNA. Extracts prepared from rad50 and rad52 mutant cells exhibited the same activity. Partial purification of this activity suggests that a protein factor with a native molecular weight of approximately 150 kDa is primarily responsible for the activity. The possibility that this supercoiling activity may be due to tracking of a protein along the intact duplex DNA is discussed.
authors.affiliation: Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, MD 21205.
authors.forename: H S
authors.initials: HS
authors.lastname: Koo
authors.forename: K
authors.initials: K
authors.lastname: Lau
authors.forename: H Y
authors.initials: HY
authors.lastname: Wu
authors.forename: L F
authors.initials: LF
authors.lastname: Liu
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004271:DNA, Fungal / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008970:Molecular Weight; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D004271:DNA, Fungal; D004278:DNA, Superhelical; D000255:Adenosine Triphosphate; D004264:DNA Topoisomerases, Type I