Component of sequence-specific heterotrimeric transcription factor (nfya-1-NF-Y and nfya-2-NF-Y) complexes which specifically recognize a 5'-CCAAT-3' box motif found in the promoters of its target genes to regulate their expression and control cellular identity in particular tissue types (PubMed:17574230). In association with the components in the NF-Y complexes, represses the expression of the T-box transcription factor tbx-2 throughout larval development, which most likely restricts its expression to certain tissues (PubMed:23933492). May act to repress txb-2 expression in conjunction with tbx-2 itself, which has an autoregulatory role (Probable). In association with the components in the nfya-1-NF-Y complex, negatively regulates the expression of the homeobox protein egl-5 to spatially restrict its expression in tissues such as the head (PubMed:17574230). May regulate egl-5 expression in association with the mes-2-mes-3-mes-6 complex (PubMed:17574230). Forms two NF-Y heterotrimeric transcription factor complexes: the nfya-1-NF-Y complex is composed of nfya-1, nfyb-1 and nfyc-1, and the nfya-2-NF-Y complex is composed of nfya-2, nfyb-1 and nfyc-1 (PubMed:17574230). Interacts with nfyb-1; the interaction is direct and is required for the interaction with either nfya-1 or nfya-2, and subsequent binding of the complex to the 5'-CCAAT-3' box motif in DNA (PubMed:17574230). Localizes to the cytoplasm of secretory cells and cell bodies of the small ganglia surrounding the pharynx. Expressed in certain parts of the gonads with high expression in fertilized oocytes in the uterus and mature oocytes from the distal to the proximal arm of the gonad, but weak expression in the syncytial ovaries and immature oocytes at the beginning of the proximal arm of the gonad (PubMed:15704008). Expressed in the excretory cell, secretory cells in the pharyngeal terminal bulb wall, in the small ganglia surrounding the pharynx and in the neurons running anteriorly to the sensory organs in the head (PubMed:15704008). Not expressed in the intestine, the hypodermis or body wall muscle surrounding the pseudocoelomic space (PubMed:15704008). Expressed in cells of the developing embryo (PubMed:15704008, PubMed:17574230). At the larval stages, weakly expressed in neurons and pharyngeal secretory cells (PubMed:15704008, PubMed:17574230). At larval stages also expressed in the developing hermaphrodite vulva and male tail (PubMed:17574230). Not expressed in the gonads in larval stages (PubMed:15704008). RNAi-mediated knockdown results in ectopic expression of the homeobox protein egl-5 in the head region (PubMed:17574230). RNAi-mediated knockdown results in ectopic expression of tbx-2 in the gut and seam cells of L4 stage larvae and adults (PubMed:23933492). Belongs to the NFYC/HAP5 subunit family.