Cyclin D3, ~34kDa, is a member of cyclin D family that promotes cell cycle progression to the DNA systhesis (S) phase. Cyclins complexed with cyclin-dependent kinases(CDKs) mediate phosphorylation of other proteins relevant to cell proliferation. Dtype cyclins and their complexing CDKs phosphorylate the retinoblastoma gene product with influences transcription of growth-controlling genes. Cyclin D3 regulates cell proliferation during hematopoiesis, carcinogenesis, and may have function in the terminally differentiated cells. In recent studies, there is reports that cyclin D3 involves in multiple myeloma and malignant precursor T cells.