Loss of arginine methylation in Saccharomyces cerevisiae leads to the dysregulation of phosphate-associated genes and processes

Hmt1p is the predominant arginine methyltransferase in Saccharomyces cerevisiae. Its substrate proteins are involved in transcription, transcriptional regulation, nucleocytoplasmic transport and RNA splicing. Functionally, Hmt1p-catalysed methylation can also modulate protein-protein interactions. Despite Hmt1p being well-characterised, the effects of its knockout on the proteome and transcriptome have not been reported. SILAC-based analyses of the hmt1 proteome, in mid-log exponential growth, revealed a decreased abundance of phosphate-associated proteins including Pho84p (phosphate transporter), Pho8p (vacuolar alkaline phosphatase), Pho3p (acid phosphatase) along with Vtc1p, Vtc3p and Vtc4p (subunits of the vacuolar transporter chaperone complex). RNA-Seq and microarray analysis revealed a downregulation of phosphate-responsive genes in hmt1, including PHO5, PHO11 and PHO12 (acid phosphatases), PHO84 and PHO89 (phosphate transporters) and VTC3 (vacuolar transporter chaperone). Consistent with these observations, we observed a dysregulation of phosphate homeostasis in hmt1, with a general decrease in extracellular phosphatase production and a decrease in total Pi in phosphate replete medium. We show that the transcription factor Pho4p, responsible for activation of the PHO pathway, can be methylated by Hmt1p at Arg-241 and is the likely cause of phosphate dysregulation in hmt1. However, the methylation of Pho4p does not affect its nucleocytoplasmic localisation. We propose that the methylation of Pho4p may affect either its capacity to multimerise, its capacity to interact with Pho2p or target DNA, or may affect Pho4p phosphorylation at Ser-242 and/or Ser 243. Our study highlights a previously unknown function of Hmt1p in the regulation of phosphate homeostasis and suggests a means by which sensing of AdoMet may affect intracellular phosphate concentration.

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Chia SZ, Lai YW, Yagoub D, Lev S, Hamey JJ, Pang CNI, Desmarini D, Chen Z, Djordjevic JT, Erce MA, Hart-Smith G, Wilkins MR