Escherichia coli rpoA mutation which impairs transcription of positively regulated systems.

The rpoA341 (phs) mutation of Escherichia coli results in decreased expression of several positively regulated operons and has been mapped to within or very near the rpoA gene encoding the alpha subunit of RNA polymerase. We have shown that plasmid-directed synthesis of the wild-type alpha subunit can complement the defective phenotypes associated with this mutation consistent with its proposed location within rpoA. This mutation was mapped by marker rescue to within a 182bp region near the 3' end of rpoA and was subsequently transferred to a plasmid by recombination in vivo. DNA sequence analysis revealed that the RpoA341 phenotype was the result of the substitution of lysine 271 by glutamate within the alpha polypeptide. We discuss this result in relation to our current understanding of the functional organization of the alpha subunit.