title: Characterization by electron microscopy of fused F-prime factors in Escherichia coli.
abstract: During previous attempts to find mutants in which incompatibility between two F-prime (F') factors of E. coli is abolished, we found that two F' factors harbored in the same cell occasionally recombined to form a single genetic unit. Thus, a fused F'trp(+)arg(+) factor was obtained from a mating of a strain carrying recA F'trp(+) with a strain carrying recA F'arg(+). In the present paper physical fusion of the two F' factors, inferred from genetic studies, is confirmed by electron microscopy. F DNA was extracted, after detergent lysis, from four fused F' strains: the parental F'trp(+) and F'arg(+) strains and three F(+) strains. This supercoiled DNA was separated on ethidium bromide-cesium chloride gradients and converted to the open circular from before electron microscopy. The contour lengths in mum of the various DNA preparations were: F'trp(+), 59.4; F'arg(+), 33.2; the four F'trp(+)arg(+) factors, 38.5, 39.6, 63.2, and 73.5: the three F factors, 31.1, 31.1, and 31.0. Thus, different fused F' factors formed from the same parental F' factors vary in length, but are shorter than the sum of the parental F' factors.
mesh_terms: D002499:Centrifugation, Density Gradient; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000096:biosynthesis; D004926:Escherichia coli / Q000378:metabolism; D005111:Extrachromosomal Inheritance; D005827:Genetics, Microbial; D008854:Microscopy, Electron; D009154:Mutation; D009690:Nucleic Acid Conformation; D013936:Thymidine / Q000378:metabolism; D014316:Tritium
chemical_list: D004269:DNA, Bacterial; D014316:Tritium; D013936:Thymidine