[Human G1/S-specific cyclin D2 protein (289 aa, 33 kD) is encoded by the human cyclin D2 (CCND2) gene. This protein is essential for control of the G1/S phase of the cell cycle. Cyclin D2 protein binds to the protein kinases CDK4 and CDK6 (which are also required for the G1/S transition) to form a serine/threonine kinase haloenzyme complex. Cyclin D2 protein both regulates these protein kinases and confers substrate specificity to this complex. It also interacts with the Rb tumor suppressor protein and plays a role in the phosphorylation of this protein. Cyclin D2 protein plays a role in the proliferation of gonadal cells and is associated with malignant transformation of these cells. High levels of this protein have been detected in both ovarian and testicular tumors. ( NCI )]