PIMT: Proteins and Enzymes

Nuclear receptor coactivators participate in the transcriptional activation of specific genes by nuclear receptors. A new nuclear receptor coactivator-interacting protein, designated PIMT, was identified from a human liver cDNA library by using the coactivator peroxisome proliferator-activated receptor-interacting protein (PRIP) as bait in a yeast 2-hybrid screen. 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. Immunofluorescence studies showed that the 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.