CDT1 (Chromatin licensing and DNA replication factor 1) is a protein that in humans is encoded by the CDT1 gene.[5][6][7][8] It is a licensing factor that functions to limit DNA from replicating more than once per cell cycle.
The protein encoded by this gene is a key licensing factor in the assembly of pre-replication complexes (pre-RC), which occurs during the G1 phase of the cell cycle. In the assembly of pre-RCs, origin recognition complexes (ORC1-6) recognize and bind to DNA replication origins. CDT1, along with the protein CDC6, are then recruited to the forming pre-RC, followed by minichromosome maintenance complexes (MCM2-7).[9]
The activity of CDT1 during the cell cycle is tightly regulated during the S phase by the protein geminin, which inhibits it, and by SCFSKP2, which ubiquinates the protein to tag it for proteasomal degradation.[10] This regulation is important in preventing relicensing, thus ensuring that DNA is only replicated once per cell cycle.
CDT1 belongs to a family of replication proteins conserved from yeast to humans. Examples of orthologs in other species include:
DNA replication factor CDT1 has been shown to interact with SKP2.[14] Cdt1 is recruited by the origin recognition complex in origin licensing. Null-mutations for CDT1 are lethal in yeast; the spores undergo mitosis without DNA replication. The overexpression of CDT1 causes rereplication in H. sapiens, which activates the Chk1 pathway, preventing entry into mitosis.[15]
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