Visualizando o RNAm enquanto o ribossomo prossegue com a tradução

quarta-feira, novembro 17, 2010

The EMBO Journal (2010) 29, 3819 - 3825 

Published online: 12 October 2010

Visualizing the transfer-messenger RNA as the ribosome resumes translation


Jie Fu1, Yaser Hashem2, Iwona Wower3, Jianlin Lei1,6, Hstau Y Liao1, Christian Zwieb4, Jacek Wower3 and Joachim Frank1,2,5

Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA
Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
Department of Animal Sciences, Auburn University, Auburn, AL, USA
Department of Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, TX, USA
Department of Biological Sciences, Columbia University, New York, NY, USA

Correspondence to:

Joachim Frank, Department of Biology, Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute at Columbia University, 650 W. 168th Street, P&S Black Building 2-221, New York, NY 10032, USA. Tel.: +1 212 305 9510; Fax: +1 212 305 9500; E-mail:

6Present address: School of Life Sciences, Tsinghua University, Beijing 100084, China

Received 13 July 2010; Accepted 22 September 2010

Bacterial ribosomes stalled by truncated mRNAs are rescued by transfer-messenger RNA (tmRNA), a dual-function molecule that contains a tRNA-like domain (TLD) and an internal open reading frame (ORF). Occupying the empty A site with its TLD, the tmRNA enters the ribosome with the help of elongation factor Tu and a protein factor called small protein B (SmpB), and switches the translation to its own ORF. In this study, using cryo-electron microscopy, we obtained the first structure of an in vivo-formed complex containing ribosome and the tmRNA at the point where the TLD is accommodated into the ribosomal P site. We show that tmRNA maintains a stable ‘arc and fork’ structure on the ribosome when its TLD moves to the ribosomal P site and translation resumes on its ORF. Based on the density map, we built an atomic model, which suggests that SmpB interacts with the five nucleotides immediately upstream of the resume codon, thereby determining the correct selection of the reading frame on the ORF of tmRNA.

Keywords: tmRNA, trans-translation, SmpB

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