The function of RGS3 (regulator of G protein signaling 3, ENSG00000138835) is as follows. Down-regulates signaling from heterotrimeric G proteins by increasing the GTPase activity of the alpha subunits, thereby driving them into their inactive GDP-bound form. Down-regulates G protein- mediated release of inositol phosphates and activation of MAP kinases. {ECO:0000269|PubMed:10749886, ECO:0000269|PubMed:11294858, ECO:0000269|PubMed:8602223, ECO:0000269|PubMed:9858594}.