Selection for reduced translation costs at the intronic 5' end in fungi.
It is generally believed that introns are not translated; therefore, the potential intronic features that may be related to the translation step (occurring after splicing) have yet to be thoroughly studied. Here, focusing on four fungi, we performed for the first time a comprehensive study aimed at characterizing how translation efficiency is encoded in introns and affects their evolution. By analysing their intronome we provide evidence of selection for STOP codons close to the intronic 5' end, and show that the beginning of introns are selected for significantly high translation, presumably to reduce translation and metabolic costs in cases of non-spliced introns. Ribosomal profiling data analysis in Saccharomyces cerevisiae supports the conjecture that in this organism intron retention frequently occurs, introns are partially translated, and their translation efficiency affects organismal fitness. We show that the reported results are more significant in highly translated and highly spliced genes, but are not associated only with genes with a specific function. We also discuss the potential relation of the reported signals to efficient nonsense-mediated decay due to splicing errors. These new discoveries are supported by population-genetics considerations. In addition, they are contributory steps towards a broader understanding of intron evolution and the effect of silent mutations on gene expression and organismal fitness.
Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel.
Zohar
Z
Zafrir
Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel.
Hadas
H
Zur
Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel The Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel tamirtul@post.tau.ac.il.
Tamir
T
Tuller
D001203:Ascomycota / Q000235:genetics; D019143:Evolution, Molecular; D007438:Introns; D008957:Models, Genetic; D014176:Protein Biosynthesis / Q000235:genetics*; D012326:RNA Splicing; D012641:Selection, Genetic
intron evolution; mRNA translation; silent mutations; splicing; transcript evolution