Component of the sequence-specific heterotrimeric transcription factor (nfya-1-NF-Y) which specifically recognizes 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 nfya-1-NF-Y complex, 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). With the components in this 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 a heterotrimeric transcription factor complex (nfya-1-NF-Y complex) composed of nfya-1, nfyb-1 and nfyc-1, which binds to 5'-CCAAT-3' box motif in the promoters of its target genes (PubMed:17574230). Interacts with the nfyb-1 and nfyc-1 dimer; the interaction is required for subsequent binding to the 5'-CCAAT-3' box motif in DNA (PubMed:17574230). Does not interact with either nfyb-1 or nfyc-1 in their monomeric form (PubMed:17574230). Interacts with mes-3 (PubMed:17574230). 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). Highly expressed in the head ganglia neurons and the developing hermaphrodite vulva and male tail (PubMed:17574230). Weakly expressed in most somatic cells (PubMed:17574230). Not expressed in the intestine, the hypodermis, body wall muscle surrounding the pseudocoelomic space, 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). Expressed at all developmental stages (PubMed:15704008, PubMed:17574230). In larvae, highly expressed in the head ganglia neurons and the developing hermaphrodite vulva and male tail, while expression in most somatic cells is weak (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 of hermaphrodites (PubMed:17574230). RNAi-mediated knockdown results in morphological defects in the male tail due to cell transformation defects whereby anterior seam cells adopt a posterior seam cell fate, which is indicated by ectopic expression of the ray-specific protein pkd-2 in the anterior mid-body region (PubMed:17574230). This leads to impaired cell identities of the rays derived from seam cells (PubMed:17574230). These animals also have defective cell transformations in the ventral cord and generate two extra serotonergic CP neurons (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 NFYA/HAP2 subunit family.