Transcription-translation coupling is a mechanism of gene expression regulation in which synthesis of an mRNA (transcription) is affected by its concurrent decoding (translation).
Coupling involves both direct physical interactions between RNA polymerase and the ribosome ("expressome" complexes), as well as ribosome-induced changes to the structure and accessibility of the intervening mRNA that affect transcription ("attenuation" and "polarity").
Unlike Escherichia coli, in Bacillus subtilis transcription significantly outpaces translation, and coupling consequently does not occur.
Functional coupling between transcription and translation is caused by direct physical interactions between the ribosome and RNA polymerase ("expressome complex"), ribosome-dependent changes to nascent mRNA secondary structure which affect RNA polymerase activity (e.g. "attenuation"), and ribosome-dependent changes to nascent mRNA availability to transcription termination factor Rho ("polarity").
The expressome is a supramolecular complex consisting of RNA polymerase and a trailing ribosome linked by a shared mRNA transcript.
[9] Formation of an expressome complex also aids transcription elongation by the trailing ribosome opposing back-tracking of RNA polymerase.
[18] While it is typically used to describe biosynthesis operons of amino acids and other metabolites, programmed transcription termination that does not occur at the end of a gene was first identified in λ phage.
Polarity serves as mRNA quality control, allowing unused transcripts to be terminated prematurely, rather than synthesized and degraded.
The potential for transcription and translation to regulate each other was recognized by the team of Marshall Nirenberg, who discovered that the processes are physically connected through the formation of a DNA-ribosome complex.
Electron micrographs of stained cell-free protein synthesis reactions revealed branched assemblies in which strings of ribosomes are linked to a central DNA fibre.