Involved in the control of the cell cycle after S phase. May bind to and activate cdk-1 and/or cdk-2 to promote cell cycle progression. Necessary for embryogenesis. Expressed in the cell lineages ABarp, C and E as well as the NSM neuroblasts. Homozygous mutants are not viable. Partial loss-of-function mutation bc416 causes cell division defects with a reduction in the number of dividing NSM neuroblasts and some embryonic lethality. Belongs to the cyclin family. Cyclin AB subfamily.