Selective Inhibition of tRNATyr Transcription by Guanosine 3′‐Diphosphate 5′‐Diphosphate

Guanosine 3'-diphosphate 5'-diphosphate (ppGpp) selectively reduces the synthesis of su+III tRNA from omega 80 psu+III DNA relative to the synthesis of omega 80 RNA in a system in vitro containing DNA and Escherichia coli RNA polymerase holoenzyme as the sole macromolecular components. The response of su+III tRNA synthesis to increasing salt and to temperature in the presence of ppGpp suggests that the nucleotide may reduce the affinity of the enzyme for su+III promoters. The Ki for the selective inhibition of tRNA synthesis by ppGpp is 4 muM in contrast to the value of 150 muM for the inhibition of rRNA synthesis.