Arginine methyltransferase affects interactions and recruitment of mRNA processing and export factors

Hmt1 is the major type I arginine methyltransferase in the yeast Saccharomyces cerevisiae and facilitates the nucleocytoplasmic transport of mRNA-binding proteins through their methylation. Here we demonstrate that Hmt1 is recruited during the beginning of the transcriptional elongation process. Hmt1 methylates Yra1 and Hrp1, two mRNA-binding proteins important for mRNA processing and export. Moreover, loss of Hmt1 affects interactions between mRNA-binding proteins and Tho2, a component of the TREX (transcription/export) complex that is important for transcriptional elongation and recruitment of mRNA export factors. Furthermore, RNA in situ hybridization analysis demonstrates that loss of Hmt1 results in slowed release of HSP104 mRNA from the sites of transcription. Genome-wide location analysis shows that Hmt1 is bound to specific functional gene classes, many of which are also bound by Tho2 and other mRNA-processing factors. These data suggest a model whereby Hmt1 affects transcriptional elongation and, as a result, influences recruitment of RNA-processing factors.