Component of the NF-Y/HAP transcription factor complex. The NF-Y complex stimulates the transcription of various genes by recognizing and binding to a CCAAT motif in promoters (By similarity). Heterotrimeric transcription factor composed of three components, nfyA, nfyB and nfyC. nfyB and nfyC must interact and dimerize for nfyA association and DNA binding (By similarity). Belongs to the NFYB/HAP3 subunit family.