KIX domain of AtMed15a, a Mediator subunit of Arabidopsis, is required for its interaction with different proteins

Med15 is an important subunit of Mediator Tail module and is characterized by a KIX domain present towards amino terminal. In yeast and metazoans, Med15 KIX domain has been found to interact with various transcription factors regulating several processes including carbohydrate metabolism, lipogenesis, stress response and multidrug resistance. Mechanism of Med15 functioning in <i>Arabidopsis</i> is largely unknown. In this study, interactome of KIX domain of <i>Arabidopsis</i> Med15, AtMed15a, was characterized. We found 45 proteins that interact with AtMed15a KIX domain, including 11 transcription factors, 3 single strand nucleic acid-binding proteins and 1 splicing factor. The third helix of the KIX domain was found to be involved in most of the interactions. Mapping of the regions participating in the interactions revealed that the activation domain of a transcription factor, UKTF1 interacted with AtMed15a KIX domain. Thus, our results suggest that in <i>Arabidopsis</i>, activation domain of transcription factors target KIX domain of AtMed15a for their transcriptional responses.

Med15是中介体尾部模块（Mediator Tail module）的重要亚基，其特征在于氨基端附近存在KIX结构域（KIX domain）。在酵母与后生动物中，已证实Med15的KIX结构域可与多种转录因子相互作用，调控碳水化合物代谢、脂肪生成、应激反应及多药耐药等诸多生物学过程。目前，拟南芥（Arabidopsis）中Med15的作用机制尚不完全明确。本研究对拟南芥Med15的同源亚型AtMed15a的KIX结构域的相互作用组进行了系统表征。经鉴定，共有45种蛋白质可与AtMed15a的KIX结构域结合，其中包括11种转录因子、3种单链核酸结合蛋白以及1种剪接因子。研究发现，KIX结构域的第三螺旋参与了绝大多数相互作用。对相互作用参与区域的定位分析显示，转录因子UKTF1的激活结构域可与AtMed15a的KIX结构域发生相互作用。综上，本研究结果表明，在拟南芥中，转录因子的激活结构域可通过靶向结合AtMed15a的KIX结构域，介导相关转录应答过程。