40S ribosomal subunits scan mRNA for the start codon by one-dimensional diffusion
- Department of Biochemistry & Biophysics at the School of Medicine and Dentistry and Center for RNA Biology, University of Rochester, Rochester, New York 14642, USA
- Corresponding authors: dmitri_ermolenko{at}urmc.rochester.edu, david_mathews{at}urmc.rochester.edu
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Handling editor: John Woolford
Abstract
During eukaryotic translation initiation, the small (40S) ribosomal subunit is recruited to the 5′ cap and subsequently scans the 5′ untranslated region (5′ UTR) of mRNA in search of the start codon. The molecular mechanism of mRNA scanning remains unclear, particularly the requirement for and identity of a translocase. Here, using GFP reporters in Saccharomyces cerevisiae, we show that order-of-magnitude variations in the length of unstructured 5′ UTRs have only modest effects on protein synthesis, whereas structured 5′ UTRs strongly inhibit translation. Thus, when not hindered by secondary structure, mRNA scanning is not rate limiting. Loss-of-function mutations in eIF4A, Ded1, and Slh1 reveal that these translational helicases are dispensable for mRNA scanning. Our data suggest that one-dimensional diffusion predominately enables 40S movement along the 5′ UTR during mRNA scanning.
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Footnotes
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↵1 Co-first authors.
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Article is online at http://www.rnajournal.org/cgi/doi/10.1261/rna.080493.125.
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Freely available online through the RNA Open Access option.
- Received April 4, 2025.
- Accepted July 15, 2025.
This article, published in RNA, is available under a Creative Commons License (Attribution 4.0 International), as described at http://creativecommons.org/licenses/by/4.0/.
