Exon junction complex components Y14 and Mago still play a role in budding yeast

Anita Boisramé,Cécile Neuvéglise,Hugo Devillers,François Brunel,Mathieu Piot,Juliette Pouch,Djamila Onésime

doi:10.1038/s41598-018-36785-3

Abstract

Since their divergence from Pezizomycotina, the mRNA metabolism of budding yeasts have undergone regressive evolution. With the dramatic loss of introns, a number of quality control mechanisms have been simplified or lost during evolution, such as the exon junction complex (EJC). We report the identification of the core EJC components, Mago, Y14, and eIF4A3, in at least seven Saccharomycotina species, including Yarrowia lipolytica. Peripheral factors that join EJC, either to mediate its assembly (Ibp160 or Cwc22), or trigger downstream processes, are present in the same species, forming an evolutionary package. Co-immunoprecipitation studies in Y. lipolytica showed that Mago and Y14 have retained the capacity to form heterodimers, which successively bind to the peripheral factors Upf3, Aly/REF, and Pym. Phenotypes and RNA-Seq analysis of EJC mutants showed evidence of Y14 and Mago involvement in mRNA metabolism. Differences in unspliced mRNA levels suggest that Y14 binding either interferes with pre-mRNA splicing or retains mRNA in the nucleus before their export and translation. These findings indicate that yeast could be a relevant model for understanding EJC function.

Highlights

IntroductionThe metabolism of messenger RNA (mRNA) is a complex, multi-step process that involves various cellular processes, from the splicing of pre-messenger RNA (pre-mRNA) in the nucleus to their nuclear export, translation in the cytoplasm, and surveillance of cytoplasmic quality-control
The metabolism of messenger RNA is a complex, multi-step process that involves various cellular processes, from the splicing of pre-messenger RNA in the nucleus to their nuclear export, translation in the cytoplasm, and surveillance of cytoplasmic quality-control
The results showed that MAGO and Y14 have been widely lost from different lineages, notably Saccharomycetaceae including S. cerevisiae, and from the CTG clade, including the human pathogen Candida albicans (Fig. 1)

Summary

Introduction

The metabolism of messenger RNA (mRNA) is a complex, multi-step process that involves various cellular processes, from the splicing of pre-messenger RNA (pre-mRNA) in the nucleus to their nuclear export, translation in the cytoplasm, and surveillance of cytoplasmic quality-control. The link between nuclear splicing and cytoplasmic NMD was first established in mammals when the presence of a PTC more than 50 nucleotides upstream of an intron was shown to efficiently trigger mRNA degradation[3]. This led to the hypothesis that spliced mRNA carry a “mark” until their translation. IBP160, an RNA helicase of the spliceosome may be required to recruit EJC core proteins to introns prior to EJC assembly[11]. Aly/REF has been defined as a peripheral EJC component that connects RNA splicing to their export[17]. Baird et al performed a whole genome RNA interference (RNAi) screen and identified ICE1 as a novel peripheral EJC factor required for EJC-enhanced NMD28

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Conclusion