Investigations of the F conjugation gene traI:traI mutants and lambdatraI transducing phages

Abstract

A series of traI point and deletion mutants of Flac, and a traM mutant, were characterised. Complementation tests with an amber Flac traI mutant confirmed their genotypes, and in addition all the traI mutants, but not the traM mutant, were complemented by pRS31 (PSC101 traDI) and EDlambda109 (lambdatraI). Judging from the efficiencies of plating of F-specific phages, none of the mutations affected pilus formation. The traI products of F and of the F-like plasmid R1 were interchangeable with each other but not with that of R100, while the traM product of F could not be replaced by those of R1 or of R100. Neither traI nor traM were needed for conjugal transfer of ColE1. Three lambda transducing phages carrying traI were isolated by in vivo or in vitro techniques, and characterised by genetic complementation tests, by analysis of the fragments produced by restriction endonucleases, and by measurement of heteroduplex molecules. The genetic structures together with the sizes and F coordinates, of the transfer regions carried by the phages were thereby determined. Comparison of the proteins synthesised in UV-irradiated cells by one of the lambdatraI phages with those made by a derivative carrying an amber traI mutation, allowed the traI product to be identified as a protein of molecular weight 174,000. In addition, the molecular weights of the traD (84,000), traS (18,000), and traT (25,000) products made by the lambdatraSTD1 phage EDlambda107 were measured. The possible roles of the traI and traM products in conjugation are discussed.