Phosphorylation of Y14 Modulates Its Interaction with Proteins Involved in mRNA Metabolism and Influences Its Methylation

Abstract

The multicomponent exon junction complex (EJC) is deposited on the spliced mRNA during pre-mRNA splicing and is implicated in several post-splicing events, including mRNA export, nonsense-mediated mRNA decay (NMD), and translation control. This report is the first to identify potential post-translational modifications of the EJC core component Y14. We demonstrate that Y14 is phosphorylated at its repeated arginine/serine (RS) dipeptides, likely by SR protein-specific kinases. Phosphorylation of Y14 abolished its interaction with EJC components as well as factors that function downstream of the EJC. A non-phosphorylatable Y14 mutant was equivalent to the wild-type protein with respect to its association with spliced mRNA and its ability in NMD activation, but the mutant sequestered EJC and NMD factors on ribosome-containing mRNA ribonucleoproteins (mRNPs). We therefore hypothesize that phosphorylation of Y14 occurs upon completion of mRNA surveillance, leading to dissociation of Y14 from ribosome-containing mRNPs. Moreover, we found that Y14 is possibly methylated at multiple arginine residues in the carboxyl-terminal domain and that methylation of Y14 was antagonized by phosphorylation of RS dipeptides. This study reveals antagonistic post-translational modifications of Y14 that may be involved in the remodeling of Y14-containing mRNPs.