Abstract
An in vitro mixed transcription system was employed to examine the possible alteration of the promoter selectivity of Escherichia 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 stimulatory 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.