RNA polymerase sigma-related proteins in Escherichia coli: detection by antibodies against a synthetic peptide.

Antibodies were raised against a synthetic tetradecameric peptide with an amino acid sequence, DLIQEGNIGLMKAV, which corresponds to the most highly conserved region of bacterial RNA polymerase sigma factors. In a Western-blot analysis of total Escherichia coli proteins, the antiserum reacted specifically with at least three proteins with apparent molecular weights of 75 kDa, 27 kDa and 23 kDa, in addition to the known sigma factors (sigma 70 and sigma 32). The majorities of sigma 70 and sigma 32 were recovered as associated forms with the RNA polymerase on glycerol gradient centrifugation, while the other cross-reacting proteins were not. Unambiguous evidence was obtained which indicated that the intracellular level of sigma 32 increased rapidly upon heat-shock, at least in the strain containing high copy numbers of the rpoH gene.