title: Physical properties and mechanism of transfer of R factors in Escherichia coli.
abstract: The physical properties of F-like and I-like R factors have been compared with those of the wild-type F factor in Escherichia coli K-12 unmated cells and after transfer to recipient cells by conjugation. The F-like R factor R538-1drd was found to have a molecular weight of 49 x 10(6), whereas the molecular weight of the I-like R factor R64drd11 was 76 x 10(6). The wild-type F factor, F1, had a molecular weight of 62 x 10(6). When conjugation experiments are performed by using donor strains carrying these derepressed F-like or I-like R factors, the transferred deoxyribonucleic acid can be isolated as a covalently closed circle from the recipient cells. This circular deoxyribonucleic acid was characterized by making use of the observation that the complementary strands of these R factors can be separated in a CsCl-poly (U, G) equilibrium gradient. The results of the strand-separation experiments show that only one of the complementary strands of the R factor is transferred from the donor to the recipient. With both the F-like and I-like R factors, this strand is the heavier strand in CsCl-poly (U, G). These results indicate that even though F-like and I-like R factors differ greatly in many properties (phage specificity, size, compatability, etc.), they are transferred by a similar mechanism.
mesh_terms: D002499:Centrifugation, Density Gradient; D002501:Centrifugation, Zonal; D002586:Cesium; D002712:Chlorides; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000032:analysis; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000032:analysis / Q000187:drug effects*; D008854:Microscopy, Electron; D008970:Molecular Weight; D010617:Phenanthridines; D010759:Phosphorus Isotopes; D011119:Polynucleotides; D013194:Staining and Labeling; D013395:Sucrose; D013936:Thymidine; D014316:Tritium
chemical_list: D002712:Chlorides; D004269:DNA, Bacterial; D010617:Phenanthridines; D010759:Phosphorus Isotopes; D011119:Polynucleotides; D014316:Tritium; D002586:Cesium; D013395:Sucrose; D013936:Thymidine