Isolation of Hfr Strains from R ⁺ and ColV2 ⁺ Strains of <i>Escherichia coli</i> and Derivation of an R′ <i>lac</i> Factor by Transduction

Abstract

Temperature-resistant revertants were isolated from Escherichia coli strains carrying a temperature-sensitive dnaA mutation (initiation of chromosome replication) and either a repressed or a derepressed F-like R factor or a ColV2 factor. Many of the revertants had all the properties of Hfr strains, with a variety of directions and origins of transfer. From one such revertant, episomes carrying the R factor and part of the lac region (R'lac) could be isolated by transduction. This system offers a good selection for Hfr strains produced by integration of various episomes and for the isolation of R' factors.