45HIGHLIGHTS 2020

Atomic structure of potato virus X, the prototype of the Alphaflexiviridae family, A. Grinzato (a), E. Kandiah (b), C. Lico (c), C. Betti (c), S. Baschieri (c)

and G. Zanotti (a), Nature Chem. Biol. 16, 564-569 (2020); https://doi.org/10.1038/ s41589-020-0502-4. (a) Department of Biomedical Sciences,

University of Padua (Italy) (b) ESRF (c) Laboratory of Biotechnology, ENEA C.R Casaccia, Rome (Italy)

[1] M.J. Adams et al. Arch. Virol. 149, 1045-1060 (2004). [2] C. Lico, E. Benvenuto & S. Baschieri, Front. Plant Sci. 6, 1009 (2015).

STRUCTURAL BASIS OF COUPLING OF TRANSCRIPTION WITH TRANSLATION

The synthesis of prokaryotic mRNAs is affected by their concurrent decoding. Using cryo-EM single-particle analysis, molecular models of RNA polymerase in contact with a trailing ribosome were determined. These shed light on how connections between molecular machineries synchronise transcription and translation rates and regulate gene expression.

PRINCIPAL PUBLICATION AND AUTHORS

REFERENCES

indicating that all Alphaflexiviridae pack RNA in the same way and suggesting that it may be possible to construct chimeric virions carrying synthetic RNAs of interest into plant cells. Indeed, the detailed knowledge of the structure

and of the way the nucleic acid interacts with the CP units opens the way for various nano- and bio- technological applications. It also offers the possibility of designing antiviral compounds able to interfere with the virus assembly.

Genetic information is expressed in two steps: first, an mRNA is transcribed using DNA as a template, and then the mRNA is translated during protein synthesis. In bacteria, these processes can occur concurrently and the ribosome, which catalyses translation, can catch up to the transcribing RNA polymerase (RNAP). Close spatial proximity of the two gene- expression machineries allows their activities to be coordinated [1].

The coupling of transcription with translation is an important gene-expression mechanism. The

pioneering ribosome promotes transcription elongation by inhibiting backtracking of RNAP. This supports genome-wide synchronisation of transcription and translation rates, and is essential to genome stability. The ribosome also conceals newly synthesised mRNAs, selectively protecting those that are translated from decay. Coupling also supports gene-specific regulatory mechanisms. The initial sequences of some bacterial genes contain programmed transcription termination signals, which are modulated by the coupling of transcription with translation.

Fig. 31: a) Cryo-EM map and structural model of a ribosome-RNAP complex. b) The central steps of gene expression visible within the complex.