Polycomb group (PcG) protein. 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 (PubMed:12077420, PubMed:15380065). Required for small-RNA-induced H3K27 trimethylation (PubMed:26365259). Interacts directly with the N-terminal domain of mes-2. Forms a heterotrimeric complex with mes-2 and mes-3. Does not interact with mes-4. In adults, it is predominantly expressed in the germline, and weakly expressed in intestinal cells. Expressed both maternally and zygotically. Expressed in all cells of early embryos. In late embryos and L1 larva, it is weakly expressed. Double RNAi-mediated knockdown together with mes-2 RNAi 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). In addition in this background in males, there is ectopic expression of egl-5 in the mid-body region including in seam cells and hypodermal nuclei, and there is ectopic ray formation (PubMed:17574230). Belongs to the WD repeat ESC family.