Acidic protein, which assembles histones into an octamer (in vitro). Involved in the regulation of the localization and the function of the septins during mitosis. Involved in the function of B-type cyclins. Component of the GIN4 complex composed of at least BNI5, CDC3, CDC10, CDC11, CDC12, GIN4, NAP1 and SHS1 which forms a ring at the bud neck (PubMed:12058072). Homodimer (in-vitro) (PubMed:16432217). Interacts with the B-type cyclin CLB2 (PubMed:7622566). Interacts with 60S ribosomal protein L18 (RPL18A or RPL18B), CKA2, CKI1, eukaryotic elongation factor 1 complex eEF1A (TEF1 or TEF2), FOL1, HSC82, HTA2, HTB2, HTZ1, KAP114, KCC4, NIS1, SSA1, SSA2, SSB1, SSC1, SHM1, SIP5 and TCO89 (PubMed:18086883). Interacts with NBA1 (PubMed:18086883). Interacts with histone H3/H4 heterodimers (PubMed:27036862). Phosphorylation by CK2 promotes the import into the nucleus. The acidic domains are probably involved in the interaction with histones. Phosphorylation by CK2 is required for normal progression through S phase. CK2 phosphorylation is not required for correct bud formation nor histone binding. Exhibits a large proportion of multinucleate cells. Elongated buds. The percentage of elongated buds is significantly increased when GIN4 or CKI1 is also deleted. Small decrease in the percentage of cells with elongated buds is observed in NAP1 and CKA2 double mutant. NAP1 and CKI1 double mutant exhibits increased sensitivity to benomyl. Increased resistance to benomyl in NAP1 and CKA2 double mutant. Present with 8070 molecules/cell in log phase SD medium. Belongs to the nucleosome assembly protein (NAP) family. NAP-I was previously referred to as AP-I.