New data have recently established that protein phosphorylation during mitosis is the result of a controlled balance between kinase and phosphatase activities and that, as for mitotic kinases, phosphatases are also regulated during cell division. This regulation is at least in part induced by the activation of the Greatwall (Gwl) kinase at mitotic entry. Activated Gwl phosphorylates its substrates cAMP-regulated phospho protein 19 (Arpp19) and α-endosulfine (ENSA), promoting their binding to and the inhibition of PP2A. Interestingly, besides the role of the Gwl-Arpp19/ENSA in the control of mitotic division, new data in yeast support the involvement of this pathway in mRNA stabilization during G 0 program initiation, although in this case the phosphatase PP2A appears not to be implicated. Finally, Gwl activity has been shown to be required for DNA checkpoint recovery. These new findings support the view that Gwl, Arpp19 and ENSA could function as the core of a new signalization pathway that, by targeting different final substrates, could participate in a variety of physiological functions.