CDK1 has been known to be the sole cyclin-dependent kinase (CDK) partner of cyclin B1 to drive mitotic progression¹. Here we demonstrate that CDK5 is active during mitosis and is necessary for maintaining mitotic fidelity. CDK5 is an atypical CDK owing to its high expression in post-mitotic neurons and activation by non-cyclin proteins p35 and p39². Here, using independent chemical genetic approaches, we specifically abrogated CDK5 activity during mitosis, and observed mitotic defects, nuclear atypia and substantial alterations in the mitotic phosphoproteome. Notably, cyclin B1 is a mitotic co-factor of CDK5. Computational modelling, comparison with experimentally derived structures of CDK–cyclin complexes and validation with mutational analysis indicate that CDK5–cyclin B1 can form a functional complex. Disruption of the CDK5–cyclin B1 complex phenocopies CDK5 abrogation in mitosis. Together, our results demonstrate that cyclin B1 partners with both CDK5 and CDK1, and CDK5–cyclin B1 functions as a canonical CDK–cyclin complex to ensure mitotic fidelity.

已知 CDK1 是细胞周期蛋白 B1 的唯一细胞周期蛋白依赖性激酶 （CDK） 伴侣，可驱动有丝分裂进程¹。在这里，我们证明 CDK5 在有丝分裂过程中是活跃的，并且是维持有丝分裂保真度所必需的。CDK5 是一种非典型 CDK，因为它在有丝分裂后神经元中高表达，并被非细胞周期蛋白 p35 和 p39 激活²。在这里，使用独立的化学遗传学方法，我们在有丝分裂期间特异性地消除了 CDK5 活性，并观察到有丝分裂缺陷、核异型性和有丝分裂磷酸化蛋白质组的实质性改变。值得注意的是，细胞周期蛋白 B1 是 CDK5 的有丝分裂辅助因子。计算建模、与 CDK-细胞周期蛋白复合物的实验衍生结构的比较以及突变分析的验证表明，CDK5-细胞周期蛋白 B1 可以形成功能性复合物。CDK5-细胞周期蛋白 B1 复合物表型拷贝的破坏 CDK5 在有丝分裂中被消除。总之，我们的结果表明，细胞周期蛋白 B1 与 CDK5 和 CDK1 合作，并且 CDK5-细胞周期蛋白 B1 作为经典的 CDK-细胞周期蛋白复合物发挥作用，以确保有丝分裂保真度。