title: Studies on plasmid replication. III. Isolation and characterization of replication-defective mutants.
abstract: Some 85 Staphylococcus aureus mutants phenotypically thermosensitive for penicillinase plasmid segregation (Seg-) have been isolated and characterized. Some of the mutations were plasmid-linked and those studied in detail were found to be defective in plasmid replication, most problbly at the initiation stage. Analysis of the segregation behavior of these mutants suggested a figure of 2.7 for the average number of plasmid copies per cell in a random culture. Other mutations were host chromosome-linked and these could be divided into at least three classes on the basis of their ability to maintain plasmids of the two different incompatibility sets: some were defective for type I plasmids, some for type II, and some for both types. One host mutant, defective in segregation of type I but not type II plasmids, was defective in polymerization of both.
mesh_terms: D002875:Chromosomes; D004261:DNA Replication; D004269:DNA, Bacterial; D005111:Extrachromosomal Inheritance; D005827:Genetics, Microbial; D009154:Mutation; D010405:Penicillinase / Q000494:pharmacology; D010641:Phenotype; D013210:Staphylococcus / Q000254:growth & development*; D013696:Temperature
chemical_list: D004269:DNA, Bacterial; D010405:Penicillinase