THE ESCHERICHIA-COLI RNA-POLYMERASE ALPHA-SUBUNIT AND TRANSCRIPTIONALACTIVATION BY BACTERIOPHAGE-LAMBDA CII-PROTEIN

Bacteriophage lambda is not able to lysogenise the Escherichia coli rp oA341 mutant. This mutation causes a single amino acid substitution Ly s271Glu in the C-terminal domain of the RNA polymerase alpha subunit ( alpha CTD). Our previous studies indicated that the impaired lysogenis ation of the rpoA341 host is due to a defect in transcriptional activa tion by the phage CII protein and suggested a role for alpha CTD in th is process. Here we used a series of truncation and point mutants in t he rpoA gene placed on a plasmid to investigate the process of transcr iptional activation by the cII gene product. Our results indicate that amino-acid residues 265, 268 and 271 in the alpha subunit may play an important role in the CII-mediated activation of the p(E) promoter (m ost probably residue 271) or may be involved in putative interactions between alpha CTD and an UP-like element near p(E) (most probably resi dues 265 and 268). Measurement of the activity of p(E)-lacZ, p(I)-lacZ and p(aQ)-lacZ fusions in the rpoA(+) and rpoA341 hosts demonstrated that the mechanism of activation of these CII-dependent promoters may be in each case different.