Regulatory subunit for cdc7 which activates its kinase activity thereby playing a central role in DNA replication and cell proliferation. Specifically required during the initiation of DNA replication in egg and during early embryonic development. The complex cdc7-dbf4b phosphorylates mcm2 and mcm4 subunits and is required for cdc45 loading. Forms a complex with cdc7. Binding of complex to chromatin is dependent on pre-replication complex assembly but is not regulated by ATR checkpoint pathways. Present early in development. During oogenesis and maturation, low levels are detected in growing oocyte stages V-VI. Expression increases significantly during oocyte maturation. After fertilization, the level decreases slowly until the mid-blastula transition (MBT, stage 8.5). A sharper decrease occurs after MBT. Not detected in embryos past stage 10 of development (at protein level). Phosphorylated. Stably phosphorylated throughout the cell cycle.