Figure 1 : A mitotic enzyme relay.

From: It takes three to find the exit

Figure 1

Grallert et al.2 report that during early mitosis, the kinase enzyme Cdk1 adds a phosphate group (P) to PP1, a phosphatase enzyme, thereby inactivating it. Active and inactive phosphatases are indicated by an open (half circle) or closed catalytic site, respectively. Cdk1 is inactivated just before the beginning of chromosome separation, causing PP1 that is bound by another phosphatase, PP2A-B55, to dephosphorylate and activate both itself and the bound PP2A-B55. Subsequently, PP2A-B55 dephosphorylates an amino-acid residue in the B56 subunit of PP2A-B56 phosphatase. This dephosphorylation is inefficient during chromosome separation, because Plk1 kinase opposes the action of PP2A-B55. At the end of chromosome separation, Plk1 is inactivated, and the resulting efficient dephosphorylation of B56 enables this subunit to recruit PP1, which subsequently activates PP2A-B56. Activation of the PP2A phosphatases results in their dissociation from PP1.