transcriptional attenuation by ribosome
transcriptional attenuation by ribosome
A type of transcriptional regulation at the level of early termination. This process can occur only in prokaryotes, where transcription of an operon into messenger RNA and translation of that mRNA into polypeptides occur simultaneously. The general principle is that alternative mRNA secondary structures occur under different physiological conditions such as available amount of a particular amino acid. One set of conditions favors early termination of transcription. In the classic example of the trp biosynthesis operon, translation of the gene for a short, trp-containing polypeptide called the trp operon leader peptide pauses either at a trp codon (if tryptophan is scarce) or the stop codon (if trp is readily available). In the former situation transcription continues, but in the latter a Rho-independent terminator forms and reduces, or attenuates, expression of the tryptophan biosynthesis genes. Although the polypeptides encoded by leader peptide genes appear not to be stable once their translation is complete, it is suggested by recent studies that their nascent polypeptide chains interact specifically with ribosomes, specific uncharged tRNAs, or other cellular components to inhibit release at the stop codon and improve the function of transcriptional attenuation as a regulatory switch.