Cohen S B, Nicol R, Stavnezer E
Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935, USA.
Oncogene. 1998 Nov 12;17(19):2505-13. doi: 10.1038/sj.onc.1202177.
sno is a member of the ski oncogene family and shares ski's ability to transform avian fibroblasts and induce muscle differentiation. Ski and Sno are nuclear proteins that form homodimers and heterodimers. Ski activates transcription of cellular and viral enhancers and we have identified a DNA binding site (GTCTAGAC) through which it represses transcription. In this work, we show that SnoN binds this site and represses transcription of reporters with this binding site as an upstream element. Using fusions with the Gal4-DNA binding domain in a heterologous reporter assay, we identify a tripartite repression domain in SnoN. A 107 amino acid stretch of the SnoN repression domain, that contains two of the subdomains, is closely related to the minimal region of Ski required for transformation. The third subdomain is unique to SnoN. By analysing deletions involving each of the subdomains, we show that subdomains II and III are also required for DNA binding and cellular transformation. We provide evidence for a quenching mechanism of transcriptional repression by which subdomain II binds to TAF(II)110.
Sno是Ski癌基因家族的成员，具有与Ski相同的转化禽成纤维细胞和诱导肌肉分化的能力。Ski和Sno是形成同二聚体和异二聚体的核蛋白。Ski可激活细胞和病毒增强子的转录，我们已鉴定出一个DNA结合位点（GTCTAGAC），它通过该位点抑制转录。在这项研究中，我们发现SnoN结合该位点并以该结合位点作为上游元件抑制报告基因的转录。在异源报告基因分析中，通过与Gal4-DNA结合结构域融合，我们在SnoN中鉴定出一个三联体抑制结构域。SnoN抑制结构域的一段107个氨基酸的序列包含两个亚结构域，与转化所需的Ski最小区域密切相关。第三个亚结构域是SnoN特有的。通过分析涉及每个亚结构域的缺失情况，我们表明亚结构域II和III对于DNA结合和细胞转化也是必需的。我们提供了转录抑制淬灭机制的证据，即亚结构域II与TAF（II）110结合。
