RNA-binding protein that regulates tissue-specific alternative splicing events by binding to 5'-UGCAUG-3' and 5'-GCACG-3' elements (PubMed:17060915, PubMed:17923701, PubMed:23468662, PubMed:33372658). Also binds to poly(A), poly(G), poly(C), or poly(U) stretches of RNA (PubMed:9927456). Plays a role in the sex determination pathway and X chromosome dosage compensation, and together with sex-1 is involved in making the distinction between one and two X-chromosomes (PubMed:7821230, PubMed:21471153, PubMed:23666922, PubMed:9217163, PubMed:9927456, PubMed:16139225, PubMed:17720939, PubMed:33372658). Binds to 5'-GCAUG-3' and 5'-GCACG-3' elements in intron 6 of the pre-mRNA of the sex-determining factor xol-1 to promote its alternative splicing and together with sex-1 negatively regulates the expression of xol-1 to promote hermaphrodite development (PubMed:9217163, PubMed:33372658). Negatively regulates the expression of the active isoform of xol-1 (isoform b) by promoting intron 6 retention and the deletion of exon 7 coding sequences in hermaphrodite embryos (PubMed:33372658). Furthermore, binding to the pre-mRNA of xol-1 can also direct the use of an alternative 3' splice site enabling the xol-1 transcript to be trans-spliced to unrelated genes on chromosome 2, which also leads to xol-1 exon 7 deletion (PubMed:33372658). Does not seem to regulate the retention of introns 1 to 5 of xol-1 pre-mRNA (PubMed:33372658). Plays a role in the association of the dosage compensation complex proteins dpy-27 and sdc-3 with the hermaphrodite X chromosomes (PubMed:16139225, PubMed:17720939). Binds to 5'-UGCAUG-3' elements in intron 7 of the pre-mRNA of unc-32 to promote its alternative splicing in neuronal tissues (PubMed:23468662). Binds to 5'-UGCAUG-3' elements in intron 4 of the pre-mRNA of egl-15 to promote its alternative splicing in body wall muscle tissues (PubMed:17060915). Promotes binding of RNA-binding protein sup-12 to target RNA (PubMed:17923701). Plays a role in male mating behavior (PubMed:9927456). Interacts with sup-12. In males and hermaphrodites expressed in a subset of cells in the head and tail (PubMed:9927456). Expressed in the pharynx, intestine and in muscles from the vulva and body wall. Expressed in males and hermaphrodites throughout development (PubMed:17923701, PubMed:9927456). Expressed in early embryos before morphogenesis (PubMed:17923701). In hermaphrodite embryos, first expressed at the 8-16 cell stage of development with expression peaking by the 100-cell stage (PubMed:9217163). Not expressed at the 550-cell stage of embryogenesis (PubMed:9217163). Males and hermaphrodites are viable and there is no change in brood size (PubMed:9217163, PubMed:17720939, PubMed:33372658). In a sex-1(y263) mutant background or a sex-1 RNAi mutant background, males are viable, but hermaphrodites have highly reduced viability due to failure of the dosage compensation complex to assemble on X chromosomes, and the surviving animals show a reduction in brood size (PubMed:17720939, PubMed:16139225, PubMed:33372658). RNAi-mediated knockdown results in a 63% reduction in the number of eggs produced (PubMed:11303786). RNAi-mediated knockdown together with sex-1 results in hermaphrodite embryonic lethality (PubMed:21471153). This hermaphrodite-specific lethality is suppressed in a sea-2 bp283 mutant or sea-1 gk799 mutant background (PubMed:21471153).