Promoter selectivity ofEscherichia coliRNA polymerase: alteration by fMet-tRNA_f^Met

An in vitro mixed transcription system was employed to examine the possible alteration of the promoter selectivity of Esherichia coli RNA polymerase by specific tRNAs. Transcription in vitro was inhibited by most of the tRNAs examined, although the extent of the inhibition differed with the tRNA species. The inhibition by tRNAs was due to competition with DNA for binding RNA polymerase. This inhibitory effect remained after charging of the tRNAs with amino acids. The charging of $tRNAfMet$ with fMet, but not with Met, abolished its inhibitory effect, and instead gave a stimulatary effect on the transcription from some promoters. These observations suggest that FMet-$tRNAfMet$ plays a specific regulatory role in the coupling of transcription to translation.