Structural basis of transcription-translation coupling and collision in bacteria

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Science  11 Sep 2020:
Vol. 369, Issue 6509, pp. 1355-1359
DOI: 10.1126/science.abb5036

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Coupling transcription and translation

In bacteria, the rate of transcription of messenger RNA (mRNA) by RNA polymerase (RNAP) is coordinated with the rate of translation by the first ribosome behind RNAP on the mRNA. Two groups now present cryo–electron microscopy structures that show how two transcription elongation factors, NusG and NusA, participate in this coupling. Webster et al. found that NusG forms a bridge between RNAP and the ribosome when they are separated by mRNA. With shortened mRNA, NusG no longer links RNAP and the ribosome, but the two are oriented so that newly transcribed mRNA can enter the ribosome. Wang et al. provide further insight into the effect of mRNA length on the complex structures. They also include NusA and show that the NusG-bridged structure is stabilized by NusA.

Science, this issue p. 1355, p. 1359


Prokaryotic messenger RNAs (mRNAs) are translated as they are transcribed. The lead ribosome potentially contacts RNA polymerase (RNAP) and forms a supramolecular complex known as the expressome. The basis of expressome assembly and its consequences for transcription and translation are poorly understood. Here, we present a series of structures representing uncoupled, coupled, and collided expressome states determined by cryo–electron microscopy. A bridge between the ribosome and RNAP can be formed by the transcription factor NusG, which stabilizes an otherwise-variable interaction interface. Shortening of the intervening mRNA causes a substantial rearrangement that aligns the ribosome entrance channel to the RNAP exit channel. In this collided complex, NusG linkage is no longer possible. These structures reveal mechanisms of coordination between transcription and translation and provide a framework for future study.

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