Fission Yeast Exon Junction Complex Orthologs Ensure the Maturation of Meiotic Transcripts During Meiosis

Abstract

Meiosis, requisite for sexual reproduction, encompasses unique processes that do not occur in vegetative cells, including precise expression of specific genes (meiotic genes). During mitotic growth, to ensure the silencing of many constitutively transcribed meiotic genes, Mmi1-NURS (Mtl1-Red1 core) complex shuttles premature meiotic RNAs to be degraded by the 3’-5’exoribonuclease activity of the nuclear exosome. However, its role for meiotic gene expression in meiosis has not been explored. Here, we report that Red5, an essential NURS subunit, interacts with Rsf1, an ortholog of eukaryotic translation initiation factor eIF4aIII in the fission yeast Schizosaccharomyces pombe. Together with Mnh1, Rnps1 and Y14, Rsf1 forms the core of the Exon Junction Complex (EJC), which is essential for transcriptional surveillance and localization of mature mRNA. Using a combination of genetic, cell biology and biochemical methods, we found that EJC orthologs and NURS are functionally connected specifically in the process of meiotic gene expression during meiosis. Mutations in both complexes exhibit severe meiotic defects, which are accompanied by a concomitant loss of stability of meiotic transcripts and impaired maturation processes such as splicing. We propose that the interaction between Rsf1 and NURS serves to mediate proper meiotic mRNA maturation upon the induction of meiosis.