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Cooperation Between Translating Ribosomes and RNA Polymerase in Transcription Elongation

Science  23 Apr 2010:
Vol. 328, Issue 5977, pp. 504-508
DOI: 10.1126/science.1184939

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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

During transcription of protein-coding genes, bacterial RNA polymerase (RNAP) is closely followed by a ribosome that translates the newly synthesized transcript. Our in vivo measurements show that the overall elongation rate of transcription is tightly controlled by the rate of translation. Acceleration and deceleration of a ribosome result in corresponding changes in the speed of RNAP. Moreover, we found an inverse correlation between the number of rare codons in a gene, which delay ribosome progression, and the rate of transcription. The stimulating effect of a ribosome on RNAP is achieved by preventing its spontaneous backtracking, which enhances the pace and also facilitates readthrough of roadblocks in vivo. Such a cooperative mechanism ensures that the transcriptional yield is always adjusted to translational needs at different genes and under various growth conditions.

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