Abstract
The presence of the ColIb plasmid in Escherichia coli cells inhibits the growth of bacteriophages BF23 and T5 (Ibf phenotype; inhibition of BF23 and T5 growth). To understand this abortive infection, we devised a method of isolating mutants that were defective in some ColIb phenotypes including Ibf. This method consisted of transduction of the tet (Tcr; tetracycline resistance) or cml (Cmr; chloramphenicol resistance) gene of plasmid R222 with phage P22 into ColIb, construction of TcrCmrIbf+ Imm+ (immunity to colicin Ib) Cib- (no production of colicin Ib) recombinants by crossing between the transductants, and isolation of deletion mutants from the recombinants by phage P1 transduction. By this procedure, pKM25-2 (TcrCmsIbf-Imm-Cib-) and pKM25-1 (TcrCmsIbf+Imm+Cib-) were isolated. Construction of the cleavage map of the ColIb plasmid by restriction endonucleases and comparative analyses of the DNA fragments produced from the mutant plasmids revealed that the genes determining Ibf and Imm mapped on a 4.60 Mdal HindIII fragment (H-3) and the gene determining Cib on a 1.71 Mdal EcoRI fragment (E-12).
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