Govindaraghavan Meera, Anglin Sarah Lea, Osmani Aysha H, Osmani Stephen A
Department of Molecular Genetics, The Ohio State University, Columbus, Ohio 43220 Molecular, Cellular, and Developmental Biology Program, The Ohio State University, Columbus, Ohio 43220.
Department of Biology, Millsaps College, Jackson, Mississippi 39210.
Genetics. 2014 Aug;197(4):1225-36. doi: 10.1534/genetics.114.165647. Epub 2014 May 15.
Mitosis is promoted and regulated by reversible protein phosphorylation catalyzed by the essential NIMA and CDK1 kinases in the model filamentous fungus Aspergillus nidulans. Protein methylation mediated by the Set1/COMPASS methyltransferase complex has also been shown to regulate mitosis in budding yeast with the Aurora mitotic kinase. We uncover a genetic interaction between An-swd1, which encodes a subunit of the Set1 protein methyltransferase complex, with NIMA as partial inactivation of nimA is poorly tolerated in the absence of swd1. This genetic interaction is additionally seen without the Set1 methyltransferase catalytic subunit. Importantly partial inactivation of NIMT, a mitotic activator of the CDK1 kinase, also causes lethality in the absence of Set1 function, revealing a functional relationship between the Set1 complex and two pivotal mitotic kinases. The main target for Set1-mediated methylation is histone H3K4. Mutational analysis of histone H3 revealed that modifying the H3K4 target residue of Set1 methyltransferase activity phenocopied the lethality seen when either NIMA or CDK1 are partially functional. We probed the mechanistic basis of these genetic interactions and find that the Set1 complex performs functions with CDK1 for initiating mitosis and with NIMA during progression through mitosis. The studies uncover a joint requirement for the Set1 methyltransferase complex with the CDK1 and NIMA kinases for successful mitosis. The findings extend the roles of the Set1 complex to include the initiation of mitosis with CDK1 and mitotic progression with NIMA in addition to its previously identified interactions with Aurora and type 1 phosphatase in budding yeast.
在模式丝状真菌构巢曲霉中，有丝分裂由必需的NIMA和CDK1激酶催化的可逆蛋白质磷酸化促进和调节。Set1/COMPASS甲基转移酶复合物介导的蛋白质甲基化也已被证明可与Aurora有丝分裂激酶一起调节芽殖酵母中的有丝分裂。我们发现，编码Set1蛋白质甲基转移酶复合物一个亚基的An-swd1与NIMA之间存在遗传相互作用，因为在没有swd1的情况下，nimA的部分失活耐受性很差。在没有Set1甲基转移酶催化亚基的情况下，也能观察到这种遗传相互作用。重要的是，CDK1激酶的有丝分裂激活剂NIMT的部分失活，在没有Set1功能时也会导致致死性，这揭示了Set1复合物与两种关键有丝分裂激酶之间的功能关系。Set1介导甲基化的主要靶点是组蛋白H3K4。组蛋白H3的突变分析表明，改变Set1甲基转移酶活性的H3K4靶残基所产生的表型与NIMA或CDK1部分功能异常时的致死性相似。我们探究了这些遗传相互作用的机制基础，发现Set1复合物在有丝分裂起始阶段与CDK1共同发挥作用，在有丝分裂进程中与NIMA共同发挥作用。这些研究揭示了Set1甲基转移酶复合物与CDK1和NIMA激酶共同参与成功有丝分裂的需求。这些发现扩展了Set1复合物的作用，除了其先前在芽殖酵母中与Aurora和1型磷酸酶的相互作用外，还包括与CDK1一起启动有丝分裂以及与NIMA一起促进有丝分裂进程。
