Trimethylguanosine Synthase (TGS1)

The PIMT cDNA encodes an 852-amino acid protein containing a 9-amino acid methyltransferase motif I (VVDAFCGVG) and an invariant segment (GXXGXXI) found in K-homology motifs of many RNA-binding proteins. Northern blot analysis demonstrated ubiquitous expression of a 3.2-kb PIMT transcript, with highest expression in heart, skeletal muscle, kidney, liver, and placenta. PIMT and PRIP proteins are colocalized in the nucleus. PIMT binds 5-adenosyl-L-methionine, the methyl donor for the methyltransfer reaction, and it also binds RNA, suggesting that it is an RNA methyltransferase. Overexpression of PIMT enhances the transcriptional activity of PPARG and RXR, and this enhancement is further stimulated by overexpression of PRIP, PIMT is a component of nuclear receptor signal transduction that acts through PRIP.