Component of the CCAAT-bound heteromer, php5 is essential for DNA-binding activity. It is essential for transcription activation of cyc1. It is the linchpin that binds to the subunit association domains (SAD) of php2 and php3 to bring these proteins together. Two complexes bind CCAAT; complex I, that consists of php2/3/5 and complex II, that consists of php2/3/5/4. Belongs to the NFYC/HAP5 subunit family.