Component of a Polycomb group (PcG) complex. PcG proteins act by forming multiprotein complexes, which are required to maintain the transcriptionally repressive state of homeotic genes throughout development. In association with the nfya-1-NF-Y complex, may play a role in repressing the expression of the homeobox protein egl-5 in tissues such as the head (PubMed:17574230). PcG proteins are not required to initiate repression, but to maintain it during later stages of development. The mes-2/mes-3/mes-6 complex may participate in the global inactivation of the X chromosomes in germline cells. The complex may act via methylation of histone H3 'Lys-27', rendering chromatin heritably changed in its expressibility. This complex is required to exclude mes-4 from the inactivated X-chromosomes in germline cells. Forms a heterotrimeric complex with the Polycomb proteins mes-2 and mes-3. Does not interact with mes-4. Interacts with nyfa-1 (PubMed:17574230). In adults, it is predominantly expressed in the germline, and weakly expressed in intestinal cells. Expressed maternally and zygotically. Expressed in all cells of early embryos. In late embryos and L1 larva, it is weakly expressed, mainly in Z2 and Z3 cells. Repressed by GLD-1, which associates with the 3'-UTR of the mRNA and prevents its translation. RNAi-mediated knockdown results in ectopic expression of the homeobox protein egl-5 in the head region (PubMed:17574230). This ectopic expression of egl-5 in the head region is enhanced in a nfya-1 bp4 mutant background (PubMed:17574230).