CryoEM ensemble reveals the mechanism of 1 ribosomal frame shifting
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| Year of publication | 2022 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | To accurately synthesize a protein, the ribosome maintains the mRNA reading frame by decoding and translocating one codon at a time. Change of the reading frame of mRNA during translation, termed frame shifting, provides a strategy to expand the coding repertoire of cells and viruses. The translating ribosome switches to an alternative reading frame, either in the forward or reverse direction, i.e., skipping or rereading one or more mRNA nucleotides, respectively. For example, 1 frame shifting (1FS) controls the expression of the essential release factor 2 in bacteria and leads to pathological expression of huntingtin in eukaryotes. How and where in the elongation cycle 1FS occurs remains poorly understood. Here we address this challenge by using cryoEM to visualize 1FS on 1FS prone mRNA sequences. We present cryoEM structures of 70S complexes, allowing visualization of elongation and translocation by the GTPase elongation factor G (EFG). Four structures with a?1FS prone mRNA reveal that frame shifting takes place during translocation of tRNA and mRNA. The 1FS prone pretranslocation complex maintains the 0 frame anticodon codon pairing resembling that in canonical elongation complexes. In the midtranslocation complex with EFG, the tRNA shifts to the 1 frame near the P site, with bulged nucleotide between the E and P site codons stabilized by G926 on the 16S rRNA. The ribosome remains frame shifted in the nearly posttranslocation state. Our findings reveal that the ribosome is predisposed for 1FS before translocation, and that frame shifting is accomplished at an intermediate stage of EFG catalysed translocation. |
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