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 and M phases. The complex CDC7-DBF4B selectively phosphorylates MCM2 subunit at 'Ser-40' 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 DBF4/DBF4A or DBF4B. Such complexes are stable upon replication stress. Predominantly found in soluble fraction but not in the chromatin-bound fraction. Widely expressed. Highly expressed in testis. Increases as cells enter in S phase through G2/M phase. The protein has a short half-life (at protein level). Phosphorylated.