Anti-Proliferating cell nuclear antigen antibodies are directed against the protein encoded by the gene PCNA in humans. The gene may also be known as PCNAR, ATLD2, DNA polymerase delta auxiliary protein, and cyclin. Structurally, the protein is reported to be 28.8 kilodaltons in mass. Based on gene name, yeast, plant, fly, canine, porcine, monkey, mouse and rat orthologs may also be found.