Dye sensitivity correlated with envelope protein changes in dye (sfrA) mutants of Escherichia coli K12 defective in the expression of the sex factor F.

Mutations of the dye gene on the E. coli chromosome result in sensitivity to the dye toluidine blue and, in male cells, cause loss of F pili, producing sterility in conjugation. Compared with its dye+ parent, a strain deleted for dye (delta dye) showed an altered sensitivity to a wide range of dyes and antibiotics which affect different intracellular processes, and hence it appeared likely that the barrier properties of the cell envelope were impaired. Unlike mutants known to be defective in LPS structure, there appeared to be no correlation between the hydrophobicity of the compounds and the sensitivity of the delta dye strain. Moreover there was no difference between dye+ and delta dye strains in their sensitivity to LPS-specific phages, and chemical and GLC analysis of LPS components revealed no difference between the two strains. Examination of outer and inner membrane proteins from isogenic strains having the delta dye deletion and the dye+ gene cloned into the plasmid pACYC184, with or without insertional inactivation of dye by the transposon gamma delta, was performed by SDS-PAGE. This revealed a number of differences in the profile of proteins from both inner and outer membranes, correlated with mutation in the dye gene. The dye gene appears to be identical to the sfrA gene, which has been shown to be required for efficient transcription of the sex factor F. It is therefore proposed that the dye (sfrA) gene product may also control the expression of chromosomal genes coding for envelope proteins.