Component of the sequence-specific heterotrimeric transcription factor (NF-Y) which specifically recognizes a 5'-CCAAT-3' box motif found in the promoters of its target genes. NF-Y can function as both an activator and a repressor, depending on its interacting cofactors. Heterotrimeric transcription factor composed of three components, NF-YA, NF-YB and NF-YC. NF-YB and NF-YC must interact and dimerize for NF-YA association and DNA binding (By similarity). Can be divided into 3 domains: the weakly conserved A domain, the highly conserved B domain thought to be involved in subunit interaction and DNA binding, and the Glu-rich C domain. Belongs to the NFYB/HAP3 subunit family.