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How bacteria translate proteins from structurally blocked mRNA

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Bacterial ribosomes require a single-stranded ribosome binding site (RBS) to initiate protein synthesis, while stable RNA structure blocks initiation. Paradoxically, structured mRNAs can still be effectively translated. Researchers at Uppsala University have now illustrated the anatomy of a "standby" site and its requirements for overcoming RNA structural problems for translation.

Bacterial protein synthesis has been studied for decades. Ribosomes need access to a single-stranded RBS to initiate translation. However, some mRNAs with stably structured RBS regions are effectively translated. About 25 years ago, the Dutch researchers proposed a new mechanism to account for this, "ribosome standby": a ribosome is bound to an accessible, unstructured region elsewhere, waits for a while and then moves to the RBS when its structure is temporarily opened. [1

9659005] In this new study, published in Proceedings of the National Academy of Sciences researchers at Uppsala University have revealed the anatomy of a standby site and reported on the key role of ribosomal protein S1 in this process. S1 binds to a standby site consisting of two elements, a single stranded region and unexpectedly a short RNA hairpin. Standby binding allows the ribosome to move through the downstream RNA structure and to access the blocked RBS.

"We felt it was time to find out how exactly a standby page looks and what is needed to make it work. An old idea that so far lacked strong direct evidence," says Cédric Romilly, the study's first author .

After studies conducted by the Wagner group for several years, they examined a short mRNA encoding a toxin, TisB. Translation of this protein is entirely dependent on a standby site located> 100 nucleotides upstream of the stable and inaccessible RBS structure. Using sophisticated biochemical methods, such as fluorescence anisotropy and UV cross-linking / RNA footprints, the researchers were able to capture the ribosome in the standby site. The experiments show that it is protein S1 that directs the ribosome to the standby site, thus likely promoting the downstream RNA structure opening to access the TisB RBS.

"This has really been a tour, but it's fun to finally understand the anatomy of a real standby site," said Professor E. Gerhart H. Wagner, lead author of the study.

More information:
Cedric Romilly et al., "The ribosomal protein S1-dependent standby site in tisB mRNA consists of a single-stranded region and a 5 & apos; 39; structural element," PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1904309116

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Uppsala university

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Ribosome standby: How bacteria translate proteins from structurally blocked mRNA (2019, July 15)
July 16, 2019
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