Frameshifting of mRNA during translation provides a strategy to expand the coding repertoire of cells and viruses. How and where in the elongation cycle +1-frameshifting occurs remains poorly understood. We describe seven ~3.5-Å-resolution cryo-EM structures of 70S ribosome complexes, allowing visualization of elongation and translocation by the GTPase elongation factor G (EF-G). Four structures with a + 1-frameshifting-prone mRNA reveal that frameshifting takes place during translocation of tRNA and mRNA. Prior to EF-G binding, the pre-translocation complex features an in-frame tRNA-mRNA pairing in the A site. In the partially translocated structure with EF-G•GDPCP, the tRNA shifts to the +1-frame near the P site, rendering the freed mRNA base to bulge between the P and E sites and to stack on the 16S rRNA nucleotide G926. The ribosome remains frameshifted in the nearly post-translocation state. Our findings demonstrate that the ribosome and EF-G cooperate to induce +1 frameshifting during tRNA-mRNA translocation.
- MeSH
- biokatalýza MeSH
- elektronová kryomikroskopie MeSH
- elongace translace peptidového řetězce genetika MeSH
- elongační faktor G chemie genetika metabolismus MeSH
- Escherichia coli genetika metabolismus MeSH
- konformace nukleové kyseliny MeSH
- konformace proteinů MeSH
- messenger RNA chemie genetika metabolismus MeSH
- molekulární modely MeSH
- posun čtecího rámce na ribozómech genetika MeSH
- proteiny z Escherichia coli chemie genetika metabolismus MeSH
- ribozomy genetika metabolismus ultrastruktura MeSH
- RNA ribozomální 16S chemie genetika metabolismus MeSH
- RNA transferová chemie genetika metabolismus MeSH
- tRNA-methyltransferasy genetika metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
Regulation of cellular iron homeostasis is crucial as both iron excess and deficiency cause hematological and neurodegenerative diseases. Here we show that mice lacking iron-regulatory protein 2 (Irp2), a regulator of cellular iron homeostasis, develop diabetes. Irp2 post-transcriptionally regulates the iron-uptake protein transferrin receptor 1 (TfR1) and the iron-storage protein ferritin, and dysregulation of these proteins due to Irp2 loss causes functional iron deficiency in β cells. This impairs Fe-S cluster biosynthesis, reducing the function of Cdkal1, an Fe-S cluster enzyme that catalyzes methylthiolation of t6A37 in tRNALysUUU to ms2t6A37. As a consequence, lysine codons in proinsulin are misread and proinsulin processing is impaired, reducing insulin content and secretion. Iron normalizes ms2t6A37 and proinsulin lysine incorporation, restoring insulin content and secretion in Irp2-/- β cells. These studies reveal a previously unidentified link between insulin processing and cellular iron deficiency that may have relevance to type 2 diabetes in humans.
- MeSH
- beta-buňky metabolismus MeSH
- homeostáza MeSH
- inzulin metabolismus MeSH
- inzulinom genetika metabolismus MeSH
- krysa rodu rattus MeSH
- myši inbrední C57BL MeSH
- myši knockoutované MeSH
- nádorové buněčné linie MeSH
- nádory slinivky břišní genetika metabolismus MeSH
- porucha glukózové tolerance genetika MeSH
- proinsulin genetika metabolismus MeSH
- proteiny obsahující železo a síru metabolismus MeSH
- regulační protein železa 2 genetika metabolismus MeSH
- RNA transferová Lys genetika metabolismus MeSH
- signální dráha UPR genetika MeSH
- tRNA-methyltransferasy genetika metabolismus MeSH
- železo metabolismus MeSH
- zvířata MeSH
- Check Tag
- krysa rodu rattus MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
