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Isolation of Hfr Strains from R⁺ and ColV2⁺ Strains of Escherichia coli and Derivation of an R'lac Factor by Transduction

¹ Department of Biology, College of General Education, Osaka University, Toyonaka, Osaka, Japan, and Départment de Biologie Moléculaire, Université de Genève, 30, quai de l'Ecole de Médecine, 1211 Genève, Switzerland

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.