Cyclin B2 (also CCNB2 and G2/mitotic-specific cyclin-B2) is a 45-46kD member of the Cyclin AB subfamily, cyclin family of proteins. It is widely expressed and associates with CDK1 providing substrate specificity to a phosphorylating complex. A phosphorCDK1:Cyclin B2 complex is associated with the Golgi apparatus, where it contributes to Golgi fragmentation during mitosis. It is also possible that Cyclin B2 can substitute for Cyclin B1 during the early stages of mitosis. Human Cyclin B2 is 398aa in length. It contains two cyclin box folds (aa201-290 and 298-383) and two substrate binding sites (aa165-254 and 264-347). Phosphorylation occurs at Ser92, Thr94, Ser99, Ser204, Ser392 and Ser398. Over aa1-101, human Cyclin B2 shares 79% aa identity with mouse Cyclin B2.