Regulatory subunit for CDC7 which activates its kinase activity thereby playing a central role in DNA replication and cell proliferation. Required for progression of S phase. The complex CDC7-DBF4A selectively phosphorylates MCM2 subunit at 'Ser-40' and 'Ser-53' and then is involved in regulating the initiation of DNA replication during cell cycle. Forms a complex with CDC7. Note that CDC7 forms distinct complex either with DBF4A or DBF4B. Such complexes are stable upon replication stress. Interacts with MEN1, MCM2, ORC2, ORC4 and ORC6. Interacts (via IBM motifs) with PSIP1 (via IBD domain); phosphorylation increases its affinity for PSIP1 (PubMed:29997176). Highly expressed in testis and thymus. Expressed also in most cancer cells lines. Induced in G1 phase at low level, increased during G1-S phase and remain high during S and G2-M phase. Phosphorylation increases its interaction with PSIP1.