Phosphorylation sites on lamin B1 promote mitotic disassembly. (A) Schematic representation of lamin B1 domain structure and phosphorylation (UniProt). The central rod is flanked by several mitotic phosphorylation sites (indicated by asterisks) that exhibit CDK1 and PKC consensus motifs (Pearson and Kemp, 1991). (B) Overview of lamin B1 reporters containing serine (S) to alanine (A) mutations at CDK1 and/or PKC consensus phosphorylation sites. (C) Confocal time-lapse microscopy images of HeLa cells stably expressing H2B-mCherry and transiently expressing the indicated lamin B1 reporter tagged with GFP (gray). Progression through mitosis was followed, and time relative to chromatin condensation in prophase is shown. Arrowheads indicate cytoplasmic lamin B1 fragments present after prometaphase. Bars, 10 µm.