The eukaryotic ribosomal protein S15/uS19 is involved in fungal development and its C-terminal tail contributes to stop codon recognition

Abstract

SummaryS15/uS19 is one of the fifteen universally conserved ribosomal proteins of the small ribosomal subunit. While prokaryotic uS19 is located away from the mRNA decoding site, cross-linking studies identified eukaryotic uS19 C-terminal tail as contacting the A site on the 80S ribosome. Here, we study the effects of uS19 mutations isolated as translation accuracy mutations in the filamentous fungusPodospora anserina. All mutations alter residues of uS19 C-terminal tail, and cluster to the eukaryote-specific decapeptide 138-PGIGATHSSR-147. All mutations modify fungal development and cytosolic translation, albeit differently. Two mutations (P138S and S145F) increase fungus longevity and display mild effects on translation, while others (G139D and G139C) decrease longevity, have stronger effects on translation and confer hypersensitivity to paromomycin. By mimickingP. anserinamutations in the yeastSaccharomyces cerevisiae RPS15gene, we further show that P138S and S145F induce hyperaccurate recognition of the three stop codons, whereas G139D and G139C impair UAG and UAA codon recognition. Noteworthy, inP. anserina, uS19 genetically interacts with the eRF1 and eRF3 release factors. All together, our data indicate that uS19 C-terminal tail contributesin vivoto eukaryotic translation termination, and identify key amino acids of uS19 that potentially modulate eRF1-eRF3 interaction in the pre-termination complex.Graphical abstractAbbreviated SummaryS15/uS19 is a conserved small ribosomal protein that in eukaryotes harbors a flexible C-terminal extension proposed to interact with the A site mRNA codon during translation. Here, we describe how C-terminal variants variously affectPodospora anserinadevelopment and longevity and impact fungal ribosome and polysome formation. We reveal that stop codon recognition is significantly altered by the presence of those C-terminal variants, which either expand or on the contrary restrict termination ambiguity.