PASTICCINO2 (PAS2) is a protein Tyr phosphatase-like member (PTPL) that is highly conserved in eukaryotes and is characterized by an inactive catalytic site of the phosphatase. PAS2 interacts directly with a cyclin-dependent kinase (CDK) in the CDK-Tyr-15 phosphorylation-dependent manner. Loss of the PAS2 function in Arabidopsis leads to dephosphorylation and enhancement of CDKA;1 activity, suggesting that PAS2, similar to other PTPL proteins, functions as an anti-phosphatase by binding the kinase and preventing its dephosphorylation by other activating phosphatases. PAS2 slows down cell division at the G2-to-M transition and holds cells in a differentiated state when overexpressed in plants. This suggests that the balance between cell division and differentiation is regulated through control of the CDKA;1 activity entailed by the PAS2 anti-phosphatase (Da Costa et al. 2006). No functional CDC25 phosphatases were found in plants so far to inactivate CDKs, and the association between PAS2 and Tyr-phosphorylated CDKs may be one of the mechanisms to regulate CDK temporal activation (Boudolf et al. 2006).
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