The function of DBF4 (DBF4-CDC7 kinase regulatory subunit, Ensembl gene identifier ENSG00000006634) is as follows. 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. {ECO:0000269|PubMed:10373557, ECO:0000269|PubMed:10523313, ECO:0000269|PubMed:17062569}.