FUNCTION Non-catalytic component of the methylosome complex, composed of PRMT5, WDR77 and CLNS1A, which modifies specific arginines to dimethylarginines in several spliceosomal Sm proteins and histones (PubMed:11756452). This modification targets Sm proteins to the survival of motor neurons (SMN) complex for assembly into small nuclear ribonucleoprotein core particles. Might play a role in transcription regulation. The methylosome complex also methylates the Piwi proteins (PIWIL1, PIWIL2 and PIWIL4), methylation of Piwi proteins being required for the interaction with Tudor domain-containing proteins and subsequent localization to the meiotic nuage (PubMed:23071334).SUBUNIT Component of the methylosome complex composed of PRMT5, WDR77 and CLNS1A (PubMed:18984161, PubMed:21081503). Found in a complex composed of PRMT5, WDR77 and RIOK1 (PubMed:21081503). RIOK1 and CLNS1A bound directly to PRMT5 at the same binding site, in a mutually exclusive manner, which allows the recruitment of distinct methylation substrates, such as nucleolin/NCL and Sm proteins, respectively (PubMed:21081503). Found in a complex with the component of the methylosome, PRMT5, CLNS1A, WDR77, PRMT1 and ERH (PubMed:25284789). Directly interacts with PRMT5, as well as with several Sm proteins, including SNRPB and SNRPD2 and, more weakly, SNRPD3 and SNRPE (PubMed:11756452, PubMed:33376131). Forms a compact hetero-octamer with PRMT5, decorating the outer surface of a PRMT5 tetramer. Interacts with SUZ12 and histone H2A/H2AC20, but not with histones H2B, H3 nor H4 (PubMed:16712789). Interacts with CTDP1 and LSM11 (PubMed:12560496, PubMed:16087681). Interacts with APEX1, AR and NKX3-1 (PubMed:12972618, PubMed:19188445). Interacts with CHTOP (PubMed:25284789). Interacts with FAM47E. Interacts with TSC22D2 (PubMed:27337956).INTERACTION Nuclear in Leydig cells and cytoplasmic in germ cells during fetal testicular development. In adult testis, predominantly nuclear. Subcellular location varies from nuclear to cytoplasmic in various tumors (PubMed:17437848).ALTERNATIVE PRODUCTS Highly expressed in heart, skeletal muscle, spleen, testis, uterus, prostate and thymus. In testis, expressed in germ cells and Leydig cells, but not in peritubular myocytes, nor in Sertoli cells. Expressed in prostate cancers, in seminomas and in Leydig cell tumors.DEVELOPMENTAL STAGE Expressed in Leydig cells during fetal testicular development, especially during the second semester. Germ cells expression is detected as early as 10 weeks of gestation.