Mutations affecting transcription pausing in the Bacillus subtilis pyr operon

Pausing during transcription of the Bacillus subtilis pyr operon was proposed to play a role in its regulation by attenuation. Substitution mutations in the B. subtilis pyr DNA specifying the 3′-terminal nucleotides of the previously identified transcription pause sites substantially reduced pausing at these sites in vitro. This result confirms the general utility of this mutagenic strategy for studying transcriptional pausing. Pyrimidine-mediated repression in vivo of pyr-lacZ fusions containing some of these substitution mutations was substantially lower than those observed with the wild-type pyr-lacZ fusions. However, these defects in regulation were correlated with alterations in the stability of the terminator stem-loop specified by the attenuator, rather than with their effects on transcriptional pausing in vitro.