Component of the SDC complex that functions in sex determination and in X chromosome dosage compensation specifically in hermaphrodite (XX) animals (PubMed:8431944, PubMed:11937488). Plays a central role in the recruitment of the condensin I-like dosage compensation complex to the male sex-determining autosomal gene her-1, thereby contributing to its repression and initiating hermaphrodite sexual development (PubMed:11937488, PubMed:14660541). Involved in the recruitment and assembly of the dosage compensation complex and the dosage compensation protein dpy-21 onto the X chromosomes in hermaphrodites, which leads to a reduction of X-linked gene transcription and an equalization of X-linked gene expression between the sexes (PubMed:14660541, PubMed:9458050, PubMed:8939870, PubMed:9056777, PubMed:8939869). Component of the SDC complex, which consists of sdc-1, sdc-2 and sdc-3 (PubMed:11937488). Within the complex, interacts with sdc-1 and sdc-2 (PubMed:11937488). Interacts with dpy-21 (PubMed:14660541). Localizes specifically to X chromosomes in hermaphrodite (XX) embryos after the 40-cell stage. Expressed in somatic and in germline tissues in hermaphrodites (XX). In males (XO), only present in embryos younger than the 100-cell stage (at protein level). Expressed in embryonic and early larval stages and in adult animals. Sumoylated. Sumoylation is important for assembly of the dosage compensation complex and its robust binding to the X chromosome. Disrupts the X-chromosome specific localization of dpy-26, mix-1 and dpy-21.