de los Santos T, Hollingsworth N M
Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, SUNY Stony Brook, Stony Brook, New York 11794-5215, USA.
J Biol Chem. 1999 Jan 15;274(3):1783-90. doi: 10.1074/jbc.274.3.1783.
The synaptonemal complex (SC) is a proteinaceous structure formed between pairs of homologous chromosomes during prophase I of meiosis. The proper assembly of axial elements (AEs), lateral components of the SC, during meiosis in the yeast, Saccharomyces cerevisiae, is essential for wild-type levels of recombination and for the accurate segregation of chromosomes at the first meiotic division. Genetic experiments have indicated that the stoichiometry between two meiosis-specific components of AEs in S. cerevisiae, HOP1 and RED1, is critical for proper assembly and function of the SC. A third meiosis-specific gene, MEK1, which encodes a putative serine/threonine protein kinase, is also important for proper AE function, suggesting that AE formation is regulated by phosphorylation. In this paper, we demonstrate that Mek1p is a functional kinase in vitro and that catalytic activity is an essential part of the meiotic function of Mek1 in vivo. Immunoblot analysis revealed that Red1p is a MEK1-dependent phosphoprotein. Co-immunoprecipitation experiments demonstrated that the interaction between Hop1p and Red1p is enhanced by the presence of MEK1. Thus, MEK1-dependent phosphorylation of Red1p facilitates the formation of Hop1p/Red1p hetero-oligomers, thereby enabling the formation of functional AEs.
联会复合体（SC）是在减数分裂前期I同源染色体对之间形成的一种蛋白质结构。在酿酒酵母减数分裂过程中，SC的侧向成分轴向元件（AE）的正确组装对于野生型水平的重组以及第一次减数分裂时染色体的准确分离至关重要。遗传实验表明，酿酒酵母中AE的两个减数分裂特异性成分HOP1和RED1之间的化学计量对于SC的正确组装和功能至关重要。第三个减数分裂特异性基因MEK1编码一种假定的丝氨酸/苏氨酸蛋白激酶，对AE的正常功能也很重要，这表明AE的形成受磷酸化调节。在本文中，我们证明Mek1p在体外是一种功能性激酶，并且催化活性是Mek1在体内减数分裂功能的重要组成部分。免疫印迹分析显示Red1p是一种MEK1依赖性磷蛋白。免疫共沉淀实验表明，MEK1的存在增强了Hop1p和Red1p之间的相互作用。因此，Red1p的MEK1依赖性磷酸化促进了Hop1p/Red1p异源寡聚体的形成，从而使功能性AE得以形成。
