Regulation of mitotic exit by a timely dephosphorylation cascade. (A) Regulation of PP2A-B55 in metaphase and during mitotic exit. See text for details (Gharbi-Ayachi et al., 2010; Cundell et al., 2013; Heim et al., 2015; Mochida, 2015; Ma et al., 2016). (B) Model for the PP2A-B55 timer of substrate recognition according to Cundell et al. (2016). Timing of substrate dephosphorylation is determined by two polybasic regions upstream and downstream of the phosphorylated threonine residue. Early spindle proteins have a more pronounced polybasic region than later nuclear envelope proteins.