title: Transition of the R factor R12 in Proteus mirabilis.
abstract: When Proteus mirabilis harboring the R factor R12 (a round of replication mutant of the R factor NR1) is cultured in medium containing streptomycin there can be an amplification in the number of copies of r-determinants per cell and the formation of enlarged polygenic R factors containing repeated sequences of r-determinants as well as polygenic molecules consisting of repeated sequences of r-determinants. This phenomenon has been referred to as the "transition." When transitioned cells are then cultured in drug-free medium, within a few generations two distinct density species of R factor deoxyribonucleic acid (DNA) are observed in a CsCl density gradient: a 1.712 g/ml band of covalently closed circular R factor DNA consisting of one transfer factor (RTF-TC) plus one r-determinant and a 1.718 g/ml band consisting of repeated sequences of r-determinants. The RTF-TC component of the R factor appears to control the replication of all the R factor DNA which is attached to it. In the autonomous state, however, polygenic sequences of r-determinants do not appear to replicate under the same control mechanism as when they are attached to an RTF-TC.
mesh_terms: D001483:Base Sequence; D002499:Centrifugation, Density Gradient; D002701:Chloramphenicol / Q000494:pharmacology; D003470:Culture Media; D004261:DNA Replication; D004269:DNA, Bacterial / Q000032:analysis / Q000096:biosynthesis*; D004270:DNA, Circular / Q000032:analysis; D004352:Drug Resistance, Microbial; D005111:Extrachromosomal Inheritance; D005796:Genes; D008970:Molecular Weight; D009154:Mutation; D011513:Proteus mirabilis / Q000032:analysis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D013307:Streptomycin / Q000494:pharmacology
chemical_list: D003470:Culture Media; D004269:DNA, Bacterial; D004270:DNA, Circular; D002701:Chloramphenicol; D013307:Streptomycin