Protein kinases direct polarized growth by regulating the cytoskeleton in time and space and could play similar roles in cell division. We found that the Cdc42-activated polarity kinase Pak1 colocalizes with the assembling contractile actomyosin ring (CAR) and remains at the division site during septation. Mutations in pak1 led to defects in CAR assembly and genetic interactions with cytokinesis mutants. Through a phosphoproteomic screen, we identified novel Pak1 substrates that function in polarized growth and cytokinesis. For cytokinesis, we found that Pak1 regulates the localization of its substrates Mid1 and Cdc15 to the CAR. Mechanistically, Pak1 phosphorylates the Mid1 N-terminus to promote its association with cortical nodes that act as CAR precursors. Defects in Pak1-Mid1 signaling lead to misplaced and defective division planes, but these phenotypes can be rescued by synthetic tethering of Mid1 to cortical nodes. Our work defines a new signaling mechanism driven by a cell polarity kinase that promotes CAR assembly in the correct time and place.

中文翻译：

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裂殖酵母 Pak1 磷酸化苯胺样 Mid1 以实现胞质分裂的空间控制

蛋白激酶通过在时间和空间上调节细胞骨架来指导极化生长，并且可以在细胞分裂中发挥类似的作用。我们发现 Cdc42 激活的极性激酶 Pak1 与组装收缩肌动球蛋白环 (CAR) 共定位，并在分隔过程中保留在分裂位点。pak1 突变导致 CAR 组装缺陷以及与胞质分裂突变体的遗传相互作用。通过磷酸化蛋白质组学筛选，我们鉴定出了在极化生长和胞质分裂中发挥作用的新型 Pak1 底物。对于胞质分裂，我们发现 Pak1 调节其底物 Mid1 和 Cdc15 在 CAR 上的定位。从机制上讲，Pak1 磷酸化 Mid1 N 末端，以促进其与充当 CAR 前体的皮质节点的关联。Pak1-Mid1 信号传导的缺陷会导致分裂平面错位和有缺陷，但这些表型可以通过 Mid1 与皮质节点的合成束缚来挽救。我们的工作定义了一种由细胞极性激酶驱动的新信号传导机制，可促进 CAR 在正确的时间和地点组装。