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

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 beta subunit. The third mutation is in the rpoC gene, encoding the beta' subunit. All three RNA polymerase mutations affect termination efficiency, even in rho+ strains, suggesting that the C-terminal end of the beta as well as the beta' subunit participates in termination. In addition we find that all three rpoBC alleles inhibit lambda N-mediated antitermination at 30 degrees 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.