Identification, characterization and chromosomal localization of the cognate human and murine DBF4 genes

The kinase Dbf4p/Cdc7p is required for the G1/S phase transition during the cell cycle and plays a direct role in the activation of individual origins of replication in Saccharomyces cerevisiae. Here, we report the identifica tion and characterization of mouse and human cDNAs whose products are relat ed in sequence to Saccharomyces cerevisiae DBF4 cDNA. Both mammalian Dbf4 p roteins contain a putative site for phosphorylation by CDK, PEST protease c leavage sites, nuclear localization signals and a short-looped zinc finger- like domain. Transcription of MmDBF4 is suppressed in mouse NIH3T3 fibrobla sts made quiescent by serum starvation. Upon replenishment of the medium, t ranscript levels increase during progression through G1, peaking as cells e nter S phase. MmDbf4p interacts physically with Cdc7p and Mcm2p in vivo. Us ing fluorescence in situ hybridization (FISH), the human DBF4 gene was loca lized to chromosome 7 (q21.3), whereas FISH mapped the murine counterpart t o band A2 on chromosome 5. The results of chromosome mapping indicate that in both mouse and human the gene is present as a single copy. The structura l conservation between Dbf4-related proteins suggests that these proteins p lay a key role in the regulation of DNA replication during the cell cycle i n all eukaryotes.