NF-YB is the beta subunit of the trimeric NFY transcription factor complex that binds a 5'-CCAAT-3' motif in promoters. It forms a tight dimer with the C subunit, a prerequisite for association with subunit A. The resulting trimer binds to DNA with high specificity and affinity, and activates the transcription of genes such as type 1 collagen, albumin, and beta-actin. Subunits B and C each contain a histone-like motif, supported by evidence from protein sequence alignments and experiments with mutants.