Cloning and insertional inactivation of the dye (sfrA) gene, mutation of which affects sex factor F expression and dye sensitivity of Escherichia coli K-12.

Deletions of the Escherichia coli K-12 chromosome between trpR and thr render the bacterium sensitive to the dye toluidine blue (Dye-), and if male (Hfr or F'), the strain is sterile (Fex-), failing to donate F' or chromosomal markers and resistant to male-specific phages as a consequence of its inability to elaborate F pili. A 6-kilobase SalI fragment of E. coli chromosomal DNA cloned into the plasmid pBR322 has been shown to complement both the Dye- and Fex- phenotypes. Insertion of the transposon gamma delta (Tn1000) into a specific part of this plasmid invariably results in both the Dye- and Fex- phenotypes, indicating that these phenotypes derive from mutation in a single gene. Complementation tests between such insertions and sfrA4, a previously isolated mutation resulting in a Fex- phenotype and reported to code for a transcriptional control factor for F (L. Beutin, P. A. Manning, M. Achtman, and N. Willetts, J. Bacteriol. 145:840-844, 1981), indicated that dye and sfrA4 were mutations in a single cistron. It is proposed that the dye (sfrA) gene product is necessary not only for efficient transcription of the F factor genes, but also for some component(s) of the bacterial envelope, loss of which results in sensitivity to toluidine blue.