Protein phosphatase 1 (PP1) is a highly conserved protein phosphatase that performs most of the serine- and threonine-dephosphorylation reactions in eukaryotes and opposes the actions of a diverse set of serine and threonine (Ser-Thr) protein kinases. PP1 gains substrate specificity through binding to a large number (>200) of regulatory proteins that control PP1 localization, activity, and interactions with substrates. PP1 recognizes the well-characterized RVxF binding motif that is present in many of these regulatory proteins, thus generating a multitude of distinct PP1 holoenzymes. We showed that a subset of the RVxF binding motifs, in which x is a phosphorylatable amino acid (RV[S/T]F), was phosphorylated specifically during mitosis and that this phosphorylation event abrogated the interaction of PP1 with the regulatory protein. We determined that this phosphorylation was primarily governed by the mitotic protein kinase Aurora B and that high phosphorylation site stoichiometry of these sites maintained the phosphorylation of PP1 substrates during mitosis by disrupting the assembly of PP1 holoenzymes. We generated an antibody that recognizes the phosphorylated form of the RV[S/T]F motif (RVp[S/T]F) and used it to identify known PP1 regulatory proteins (KNL1, CDCA2, and RIF1) and multiple proteins that could potentially act as PP1 binding partners (UBR5, ASPM, SEH1, and ELYS) governed by this mechanism. Together, these data suggest a general regulatory mechanism by which the coordinated activities of Aurora B and PP1 control mitotic progression.

蛋白磷酸酶1（PP1）是高度保守的蛋白磷酸酶，它在真核生物中执行大多数丝氨酸和苏氨酸去磷酸化反应，并且反对多种丝氨酸和苏氨酸（Ser-Thr）蛋白激酶的作用。PP1通过与大量控制PP1定位，活性以及与底物相互作用的调节蛋白结合而获得底物特异性。PP1识别许多这些调节蛋白中存在的特征明确的RVxF结合基序，从而产生大量不同的PP1全酶。我们显示，其中有一个是RVxF结合基序的子集，其中x是可磷酸化的氨基酸（RV [S / T] F），在有丝分裂期间被特定地磷酸化，并且该磷酸化事件消除了PP1与调节蛋白的相互作用。我们确定这种磷酸化主要受有丝分裂蛋白激酶Aurora B支配，并且这些位点的高磷酸化位点化学计量通过破坏PP1全酶的组装，在有丝分裂过程中维持PP1底物的磷酸化。我们生成了识别RV [S / T] F基序（RVp [S / T] F）磷酸化形式的抗体，并用它来识别已知的PP1调节蛋白（KNL1，CDCA2和RIF1）以及多种可以可能会充当受此机制控制的PP1绑定伙伴（UBR5，ASPM，SEH1和ELYS）。总之，这些数据表明了一种一般的调节机制，通过该机制，Aurora B和PP1的协调活动可控制有丝分裂的进程。