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A NusE:NusG Complex Links Transcription and Translation

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Science  23 Apr 2010:
Vol. 328, Issue 5977, pp. 501-504
DOI: 10.1126/science.1184953

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Transcription and Translation in Train

In bacteria, translation of messenger RNA into proteins by the ribosome usually begins soon after the ribosome binding site emerges from RNA polymerase. Now there is evidence for direct coupling between transcription and translation in bacteria. Proshkin et al. (p. 504; see the Perspective by Roberts) show that the trailing ribosome controls the rate of transcription by preventing RNA polymerase from spontaneous backtracking, which allows precise adjustment of transcriptional yield to translational needs under various growth conditions. Burmann et al. (p. 501; see the Perspective by Roberts) provide a potential mechanism for coupling by showing that the transcription factor NusG, which binds RNA polymerase through its amino-terminal domain, competitively binds either a ribosomal protein or the Rho transcription termination factor through its carboxy-terminal domain. Rho binding might occur after release of the ribosome from messenger RNA, thus linking termination of transcription and translation.

Abstract

Bacterial NusG is a highly conserved transcription factor that is required for most Rho activity in vivo. We show by nuclear magnetic resonance spectroscopy that Escherichia coli NusG carboxyl-terminal domain forms a complex alternatively with Rho or with transcription factor NusE, a protein identical to 30S ribosomal protein S10. Because NusG amino-terminal domain contacts RNA polymerase and the NusG carboxy-terminal domain interaction site of NusE is accessible in the ribosomal 30S subunit, NusG may act as a link between transcription and translation. Uncoupling of transcription and translation at the ends of bacterial operons enables transcription termination by Rho factor, and competition between ribosomal NusE and Rho for NusG helps to explain why Rho cannot terminate translated transcripts.

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