Figure 2. A lysine mutant of cyclin B1 that is degraded slightly less efficiently can halt mitotic exit after the metaphase-to-anaphase transition. (A) Schematic overview of cyclin B1 mutants. The position of the Lysine-rich region is indicated; (B) Cells that arrest after transfection with Δ52–85-cyclin B1-Cerulean first progress from metaphase to anaphase, before getting stuck in a late anaphase arrest. In the cell indicated with the red arrow, sister chromatid separation is indicated, after which the cell arrests, the cleavage furrow regresses and the separated sister chromatids move back to the equatorial plane of the cell. The cell indicated with the yellow arrow, however, manages to degrade the cyclin B1 mutant and subsequently divides normally. Roughly 50% of the cells expressing this Lysine mutant of cyclin B1 arrest in anaphase.