Three rpoBC mutations that suppress the termination defects of rho mutants also affect the functions of nusA mutants

Summary We have mapped three Escherichia coli RNA polymerase mutations selected by Guarente (1979) to suppress the termination defects of rho201. We find that two of the mutations are located in the 3 half of the rpoB gene encoding the subunit. The third mutation is in the rpoC gene, encoding the subunit. All three RNA polymerase mutations affect termination efficiency, even in rho ⁺ strains, suggesting that the C-terminal end of the as well as the subunit participates in termination. In addition we find that all three rpoBC alleles inhibit N-mediated antitermination at 30° C in a strain containing the nusA1 allele. It may be significant that the three other RNA polymerase mutations known to revert the termination defect of mutant rho alleles also affect N-mediated antitermination in nusA1 strains. The correlation of these two phenotypes suggests that both phenotypes may arise from the same functional defect in RNA polymerase.     

Genetic fusions that help define a transcription termination region in Escherichia coli

The trpA gene product was analyzed from a class of strains of Escherichia coli K12 in which the lac operon has been fused by deletion to the trp operon. These are strains that have retained the ability to synthesize tryptophan. Two of these strains are shown to make a wild-type trpA product; these strains retain intact all structural genes of the ttrp operon. It is proposed that the lac operon in these strains is fused to a region of the trp operon between trpA, the last gene in the operon, and the region where trp messenger RNA synthesis terminates. The region where trp messenger RNA synthesis terminates thus is distinct from the trp structural genes.