US5/Rps2 residues at the 40S ribosome entry channel enhance initiation at suboptimal start codons in vivo. Issue 1 (18th October 2021)

• Record Type: Journal Article
• Authors: Dong, Jinsheng; Hinnebusch, Alan G
• Editors: Mitchell, A
• Is Part Of: Genetics. Volume 220:Issue 1(2022)
• Publication Date: 2021-10-18
• Subjects: initiation -- accuracy -- regulation -- scanning -- ribosome -- uS5 -- Rps2 -- yeast; Genetics -- Periodicals; 576.5
• DOI: 10.1093/genetics/iyab176
• Languages: English
• ISSNs: 0016-6731

Abstract

Abstract: The eukaryotic 43S pre-initiation complex (PIC) containing Met-tRNA i Met in a ternary complex (TC) with eIF2-GTP scans the mRNA leader for an AUG codon in favorable "Kozak" context. AUG recognition triggers rearrangement of the PIC from an open conformation to a closed state with more tightly bound Met-tRNA i Met . Yeast ribosomal protein uS5/Rps2 is located at the mRNA entry channel of the 40S subunit in the vicinity of mRNA nucleotides downstream from the AUG codon or rRNA residues that communicate with the decoding center, but its participation in start codon recognition was unknown. We found that nonlethal substitutions of conserved Rps2 residues in the entry channel reduce bulk translation initiation and increase discrimination against poor initiation codons. A subset of these substitutions suppress initiation at near-cognate UUG start codons in a yeast mutant with elevated UUG initiation, and also increase discrimination against AUG codons in suboptimal Kozak context, thus resembling previously described substitutions in uS3/Rps3 at the 40S entry channel or initiation factors eIF1 and eIF1A. In contrast, other Rps2 substitutions selectively discriminate against either near-cognate UUG codons, or poor Kozak context of an AUG or UUG start codon. These findings suggest that different Rps2 residues are involved in distinct mechanisms involved in discriminating against different features of poor initiation sites in vivo . Abstract : In eukaryotic protein synthesis, a preinitiation complex comprising the 40S ribosomal subunit, initiation factors, and initiator tRNAi scans the mRNA leader for an AUG codon in favorable context. The 40S protein uS5 (yeast Rps2) resides in the entry channel, but its role in start codon selection was unknown. Hinnebusch and Dong find that substituting uS5 residues near the entry channel increases discrimination against non-AUG codons and/or poor sequence context, both features of suboptimal start sites, implicating uS5/Rps2 in initiation accuracy.