second cyclin box found in cyclin-O (CCNO) and similar proteins
This subfamily is composed of CCNO and similar proteins including Schizosaccharomyces pombe meiosis-specific cyclin rem1, Drosophila melanogaster G2/mitotic-specific cyclin-A (CCNA), and Candida albicans G1/S-specific cyclin CCN1, among others. Rem1 is required for pre-meiotic DNA synthesis and S phase progression. CCNA is essential for the control of the cell cycle at the G2/M (mitosis) transition. CCN1 is essential for the control of the cell cycle at the G1/S (start) transition and for maintenance of filamentous growth. CCNO is specifically required for generation of multiciliated cells, possibly by promoting a cell cycle state compatible with centriole amplification and maturation. It is involved in the activation of cyclin-dependent kinase 2. Members of this subfamily contain two cyclin boxes. This model corresponds to the second one. The cyclin box is a protein binding domain.