Structure-informed mutagenesis identifies a conserved region critical for mouse insulin receptor 5'UTR IRES function.

Cells under stress shift their proteome by repressing cap-dependent translation initiation. RNA elements called internal ribosome entry sites (IRES) can allow key cellular transcripts to remain efficiently translated to support an effective stress response. Well- characterized IRESes depend on RNA structures that reduce the protein requirements for translation initiation, thus circumventing translation inhibition. We have previously determined that the insulin receptor 5' untranslated region (5'UTR) possesses a capacity for IRES activity that is conserved from insects to mammals. There are several prominent examples of viral IRES structures solved in solution; however, the RNA secondary structures of cellular IRESes remain mostly elusive, especially Background: The RNA structural requirements for cap-independent translation initiation facilitated by the Results: RNA secondary structure probing of the Insr 5'UTR in cells provides a folding model used to identify elements required for cap-independent translation initiation. Conclusion: A small region of the Insr 5'UTR distal to the translation start codon is necessary for cap-independent translation initiation and is fully sufficient in the proper structural context.