title: Comparisons of F factors and R factors: existence of independent regulation groups in F factors.
abstract: The similarity of sex pili mediated by F factors and R(fi(+)) factors and the ability of R(fi(+)) factors to control by repression the functioning of pilus genes encoded by the F factor suggested that F factors and R(fi(+)) factors are closely related. Further comparisons of the episomal properties of F factors and R(fi(+)) factors, however, indicated many differences. F factors contain information for a restriction system for phages phiII and T7. Cells containing R factors are sensitive to these phages. Furthermore, R(fi(+)) factors do not repress the F factor phiII restriction system in cells containing both an R(fi(+)) factor and an F factor. R factors and F factors are heteroimmune episomes. In addition, an R(fi(+)) factor in cells containing both an R factor and an F factor does not fully repress the expression of F-factor immunity to an incoming second F factor. R-factor and F-factor replication systems are not identical. Wild-type F-factor replication genes will complement the mutant F(ts114)lac(+) replication genes in cells containing two F factors. The F(ts114)lac(+) episome is retained when these cells are grown at 42 C; however, cells containing an R(fi(+)) factor and F(ts114)lac(+) lose the F(ts114)lac(+) when grown at 42 C, at the same rate as cells containing only the F(ts114)lac(+). The replication system of the R(fi(+)) factor will not complement the mutant F(ts114)lac(+) replication system.
mesh_terms: D001435:Bacteriophages / Q000254:growth & development; D002701:Chloramphenicol / Q000494:pharmacology; D004261:DNA Replication; D004269:DNA, Bacterial; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development; D005298:Fertility; D005816:Genetic Complementation Test; D005827:Genetics, Microbial; D009154:Mutation; D013307:Streptomycin / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D013696:Temperature; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D004269:DNA, Bacterial; D013449:Sulfonamides; D002701:Chloramphenicol; D013752:Tetracycline; D013307:Streptomycin