first cyclin box found in G2/mitotic-specific cyclin-B3 (CCNB3) and similar proteins
CCNB3 is a mitotic B-type cyclin that promotes the metaphase-anaphase transition. It controls anaphase onset independent of spindle assembly checkpoint in meiotic oocytes. CCNB3 contains two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.