A novel pleiotropic mutation in Escherichia coli K12 which affects transduction, transformation and rates of mutation.

A mutant strain of Escherichia coli K12, R2721, has been shown to differ from its parent strain, S491, in four associated phenotypic characters as a result of a single mutation. This strain did not give recombinants with DNA transduced by bacteriophage PI or bacteriophage Mu, nor transformats after exposure to R factor DNA: lysates of bacteriophage PI grown on this strain did not appear to contain any transducing particles when tested on normal recipients. Moreover, the reversion rates, both spontaneous and ultraviolet-induced, for two auxotrophic markers were reduced. The frequency of revertants was at least two orders of magnitude lower in cultures of R2721 than in cultures of S491I. Many of the rare revertants for one or other of the auxotrophic markers were found to have regained normal reversion frequencies for the other marker and for the capacity to be transduced. In all other respects, recombination in R2721 appeared normal, the frequency of chromosomal mobilization by and F' factor was unaffected and normal yields of recombinants were obtained from matings with Hfr strains. The only circumstance in which transduction of R2721 was observed was when the capacity to ferment galactose was selected and PI had been grown on a strain carrying lambdadgal when, presumably, integration was effected by the phage-coded gene products. The mutation has been located on the E. coli chromosone map between tonA and pro and has been given the symbol tdi (transduction inhibition). Double mutants, (tdi recA) and (tdi recB), have been isolated and show no unexpected properties.