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RF2 frameshift window is used to display the premature release of the E site tRNA (ribonucleic acid) from the ribosome, which is coupled with high-level frameshifting. The plus 1 frameshift event is prevented due to the presence of the E site tRNA, thus indicating the importance of E site for reading-frame maintenance.

Plastid-specific ribosomal proteins (PSRPs) have been proposed to play roles in the light-dependent regulation of chloroplast translation. Here we demonstrate that PSRP1 is not a bona fide ribosomal protein, but rather a functional homologue of the Escherichia coli cold-shock protein pY. Three-dimensional Cryo-electron microscopic (Cryo-EM) reconstructions reveal that, like pY, PSRP1 binds within the intersubunit space of the 70S ribosome, at a site overlapping the positions of mRNA and A- and P-site tRNAs. PSRP1 induces conformational changes within ribosomal components that comprise several intersubunit bridges, including bridge B2a, thereby stabilizes the ribosome against dissociation. We find that the presence of PSRP1/pY lowers the binding of tRNA to the ribosome. Furthermore, similarly to tRNAs, PSRP1/pY is recycled from the ribosome by the concerted action of the ribosome-recyding factor (RRF) and elongation factor G (EF-G). These results suggest a novel function for EF-G and RRF in the post-stress return of PSRP1/pY-inactivated ribosomes to the actively translating pool. [ABSTRACT FROM AUTHOR]