The CCNA family includes two A-type cyclins, CCNA1 and CCNA2. CCNA1 may primarily function in the control of the germline meiotic cell cycle and additionally in the control of mitotic cell cycle in some somatic cells. CCNA2 controls both the G1/S and the G2/M transition phases of the cell cycle. Members in this family contain two cyclin boxes. This model corresponds to the second one. The cyclin box is a protein binding domain.