CDC6 homolog is a protein (chains of amino acids), it localizes in the cell nucleus during cell cycle and is essential in DNA replication.
Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific 3D structure that determines its activity. It localizes in the cell nucleus during cell cycle phase G1, but translocates to the cytoplasm at the start of S phase. Cell division control protein 6 homolog is a protein that in humans is encoded by the CDC6 gene. This protein functions as a regulator at the early steps of DNA replication. 
