RGS5 is a member of the RGS superfamily and acts as a negative regulator of heterotrimeric G protein-mediated signalling through G protein-coupled receptors (GPCRs). The regulator of G-protein signaling (RGS) proteins have recently been identified as signal transduction molecules which have structural homology to SST2 of Saccharomyces cerevisiae and EGL-10 of Caenorhabditis elegans. The messenger RNA of hRGS5 was abundantly expressed in heart, lung, skeletal muscle, and small intestine, and at low levels in brain, placenta, liver, colon, and leukocytes.