POLZ encodes an expected protein of 3,130 residues, about twice the size of the yeast protein, which has 1,504 amino acids. The 2 proteins are 29% identical in an amino-terminal region of approximately 340 residues, 39% identical in a carboxy-terminal region of approximately 850 residues, and 29% identical in a 55-residue region in the middle of the 2 genes. The sequence of the expected protein strongly predicted that it is the catalytic subunit of a DNA polymerase of the polymerase-zeta type; the carboxy-terminal domain possesses, in the right order, the 6 motifs characteristic of eukaryotic DNA polymerases, most closely resembles yeast polymerase-zeta among all polymerases in the GenBank database, and is different from the human alpha (POLA), delta (POLD1), and epsilon (POLE) enzymes.