title: Increased production of a knotted form of plasmid pBR322 DNA in Escherichia coli DNA topoisomerase mutants.
abstract: Plasmid pBR322 prepared from Escherichia coli strains carrying deletion of the DNA topoisomerase I gene (delta topA) with a compensatory mutation of the DNA gyrase gene (gyrA or gyrB) and from their TopA+ transductants was analyzed by agarose gel electrophoresis followed by electron microscopy, and compared with that from isogenic wild-type strains. It was found that about 1% of the plasmid DNA molecules was a knotted species in the topA+ gyr+ strains W3110 and DM4100, while strains DM750 (delta topA gyrA224), DM800 (delta topA gyrB225), SD275 (topA+ gyrA224) and SD108 (topA+ gyrB225) produced six to ten times as much knotted DNA as the topA+ gyr+ controls. The results suggest that the increased production of knotted pBR322 DNA is closely related to mutations of the gyrase genes.
authors.affiliation: Department of Life Science, Faculty of Science, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Shishido
authors.forename: N
authors.initials: N
authors.lastname: Komiyama
authors.forename: S
authors.initials: S
authors.lastname: Ikawa
mesh_terms: D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D004269:DNA, Bacterial / Q000096:biosynthesis*; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D009154:Mutation; D010957:Plasmids
chemical_list: D004269:DNA, Bacterial; D004264:DNA Topoisomerases, Type I