Distinct uS11/Rps14 interactions with the translation preinitiation complex differentially alter the accuracy of start codon recognition.

Abstract

The eukaryotic 43S pre-initiation complex (PIC), containing methionyl initiator transfer RNA (Met-tRNAiMet) in a ternary complex (TC) with eIF2-GTP, scans the messenger RNA (mRNA) leader for an AUG start codon in favorable "Kozak" context. Recognition of AUG triggers the rearrangement of the PIC from an open scanning conformation to a closed arrested state with more tightly bound Met-tRNAiMet. Cryo-EM reconstructions of yeast PICs suggest remodeling of the interaction between 40S protein uS11/Rps14 with ribosomal RNA (rRNA) and mRNA between open and closed states; however, its importance in start codon recognition was unknown. uS11/Rps14-L137 substitutions disrupting rRNA contacts favored in the open complex increase initiation at suboptimal sites, and L137E stabilizes TC binding to PICs reconstituted in vitro with a UUG start codon, all indicating inappropriate rearrangement to the closed state at suboptimal initiation sites. Conversely, uS11/Rps14-R135 and -R136 substitutions perturbing interactions with rRNA exclusively in the closed state confer the opposite phenotypes of initiation hyperaccuracy, and for R135E, accelerated TC dissociation from reconstituted PICs. Thus, distinct interactions of uS11/Rps14 with rRNA stabilize first the open and then the closed conformation of the PIC to influence the accuracy of initiation in vivo.