Eberhard D, Busslinger M
Research Institute of Molecular Pathology, Vienna, Austria.
Cancer Res. 1999 Apr 1;59(7 Suppl):1716s-1724s; discussion 1724s-1725s.
Pax-5 codes for the transcription factor BSAP, which plays an important role in midbrain patterning, B cell development, and lymphoma formation. Pax-5 is known to control gene expression by recognizing its target genes via the NH2-terminal paired domain and by regulating transcription through a COOH-terminal regulatory module consisting of activating and inhibitory sequences. The central region of Pax-5 contains a sequence with significant homology to the first alpha-helix of the paired-type homeodomain. This partial homeodomain has been highly conserved throughout vertebrate evolution because it is found not only in Pax-5 but also in the related Pax-2 and Pax-8 members of the same Pax subfamily. Here we report that the partial homeodomain binds the TATA-binding protein (TBP) and retinoblastoma (Rb) gene product. Both TBP and Rb were shown by coimmunoprecipitation experiments to directly associate with Pax-5 in vivo. The conserved core domain of TBP and the pocket region as well as COOH-terminal sequences of Rb are required for interaction with the partial homeodomain of Pax-5 in in vitro binding assays. Furthermore, Pax-5 was specifically bound only by the underphosphorylated form of Rb. These data indicate that Pax-5 is able to contact the basal transcription machinery through the TBP-containing initiation factor TFIID, and that its activity can be controlled by the cell cycle-regulated association with Rb.
Pax-5编码转录因子BSAP，其在中脑模式形成、B细胞发育和淋巴瘤形成中发挥重要作用。已知Pax-5通过其NH2末端配对结构域识别靶基因并通过由激活和抑制序列组成的COOH末端调节模块调节转录来控制基因表达。Pax-5的中央区域包含一个与配对型同源结构域的第一个α-螺旋具有显著同源性的序列。这个部分同源结构域在整个脊椎动物进化过程中高度保守，因为它不仅存在于Pax-5中，也存在于同一Pax亚家族的相关Pax-2和Pax-8成员中。在此我们报告，这个部分同源结构域结合TATA结合蛋白（TBP）和成视网膜细胞瘤（Rb）基因产物。共免疫沉淀实验表明，TBP和Rb在体内均与Pax-5直接相关。在体外结合试验中，TBP的保守核心结构域和口袋区域以及Rb的COOH末端序列是与Pax-5的部分同源结构域相互作用所必需的。此外，Pax-5仅与Rb的低磷酸化形式特异性结合。这些数据表明，Pax-5能够通过含TBP的起始因子TFIID与基础转录机制接触，并且其活性可以通过与Rb的细胞周期调节关联来控制。
