Required for S phase entry of the cell cycle. Frequently detected in granular vesicles, in the cytoplasm of some epithelial, stromal and sperm cells and in varicosities lining nervous fibers, while it appears to be absent in endothelial and smooth muscle cells (at protein level). Widely expressed. Expressed at high level in testis. Phosphorylated. The Val-109 variant is degraded by the proteasome suggesting that it is polyubiquitinated. Belongs to the CDC123 family.