Pfitzner E, Becker P, Rolke A, Schüle R
Institut für Experimentelle Krebsforschung, Klinik für Tumorbiologie, Universität Freiburg, Germany.
Proc Natl Acad Sci U S A. 1995 Dec 19;92(26):12265-9. doi: 10.1073/pnas.92.26.12265.
The Epstein-Barr virus-encoded protein BZLF1 is a member of the basic leucine zipper (bZip) family of transcription factors. Like several other members of the bZip family, transcriptional activity of BZLF1 is modulated by retinoic acid receptors (RARs). We present evidence that the RAR alpha and BZLF1 can reciprocally repress each other's transcriptional activation by a newly discovered mechanism. Analysis of RAR alpha mutants in transfection studies reveals that the DNA binding domain is sufficient for inhibition of BZLF1 activity. Analysis of BZLF1 mutants indicates that both the coiled-coil dimerization domain and a region containing the transcriptional activation domain of BZLF1 are required for transrepression. Coimmunoprecipitation experiments demonstrate physical interactions between RAR alpha and BZLF1 in vivo. Furthermore, glutathione S-transferase-pulldown assays reveal that these protein-protein interactions are mediated by the coiled-coil dimerization domain of BZLF1 and the DNA binding domain of RAR alpha. While RAR alpha is unable to recognize BZLF1 binding sites, the RAR alpha can be tethered to the DNA by forming a heteromeric complex with BZLF1 bound to DNA. Tethering RARs via protein-protein interactions onto promoter DNA suggest a mechanism through which RARs might gain additional levels of transcriptional regulation.
爱泼斯坦-巴尔病毒编码的蛋白BZLF1是转录因子碱性亮氨酸拉链（bZip）家族的成员。与bZip家族的其他几个成员一样，BZLF1的转录活性受视黄酸受体（RAR）调节。我们提供的证据表明，RARα和BZLF1可通过一种新发现的机制相互抑制对方的转录激活。在转染研究中对RARα突变体的分析表明，DNA结合结构域足以抑制BZLF1的活性。对BZLF1突变体的分析表明，BZLF1的卷曲螺旋二聚化结构域和包含转录激活结构域的区域对于反式抑制都是必需的。免疫共沉淀实验证明了RARα和BZLF1在体内存在物理相互作用。此外，谷胱甘肽S-转移酶下拉实验表明，这些蛋白质-蛋白质相互作用是由BZLF1的卷曲螺旋二聚化结构域和RARα的DNA结合结构域介导的。虽然RARα无法识别BZLF1结合位点，但RARα可通过与结合在DNA上的BZLF1形成异源复合物而被拴系到DNA上。通过蛋白质-蛋白质相互作用将RAR拴系到启动子DNA上，提示了一种RAR可能获得额外转录调控水平的机制。
