Transcription of the E. coli tufB gene: cotranscription with four tRNA genes and inhibition by guanosine-5'-diphosphate-3'-diphosphate

Abstract

The transcription of the tufB gene by purified RNA polymerase holoenzyme was studied using the transducing phage lambda rifd 18 DNA and the hybrid plasmid pTUB1 DNA (Miyajima et al. 1979) as templates. The size of tufB mRNA synthesized in this system was about 1,700 nucleotides, and the same strand as for rrnB was transcribed. By electron microscopic examination of the R-loop formed between lambda fus3 DNA and tufB mRNA synthesized under the direction of pTUB1 DNA, it was found that the untranslated sequence of about 500 nucleotides is at the 5' end of tufB mRNA. The sequencing of the 5' region of tufB mRNA synthesized on the truncated template has revealed that the tufB gene is cotranscribed with its upstream genes for four tRNAs (thrU, tyrU, glyT, and thrT). The synthesis of this mRNA molecule is completely abolished by low concentrations of ppGpp. Neither pppGpp, ppGp, nor pGpp was effective as inhibitor in this cell-free system.