A MUTATION IN THE DSBA GENE CODING FOR PERIPLASMIC DISULFIDE OXIDOREDUCTASE REDUCES TRANSCRIPTION OF THE ESCHERICHIA-COLI OMPF GENE

An insertion mutation in the Escherichia coli dsbA gene, coding for periplasmic disulfide oxidoreductase, dramatically reduces the level of OmpF porin protein in the cell envelope. Studies with chromosomal ompF-lacZ operon and gene fusions indicate that this is due to reduced ompF transcription. Identical effects resulted from growth in medium containing the reducing agent dithiothreitol, but the combined effects of the reducing agent and dsbA were no greater than the effects of each individually. The dsbA mutation did not prevent normal regulation of ompF transcription by the local anaesthetic procaine or by osmolarity. OmpF does not contain a cysteine residue, and the sole cysteine residue in the cytoplasmic membrane regulator of ompF transcription, EnvZ, is predicted to be located on the cytoplasmic side of the membrane, and is therefore unlikely to be involved in the effects of the dsbA mutation. The effects of the dsbA mutation and of the reducing agent on ompF transcription may be due to the failure to from an essential disulfide bond in an as yet unidentified envelope protein that affects ompF transcription.