Walhout A J, Gubbels J M, Bernards R, van der Vliet P C, Timmers H T
Laboratory for Physiological Chemistry, Utrecht University, PO Box 80042, 3508 TA Utrecht, The Netherlands.
Nucleic Acids Res. 1997 Apr 15;25(8):1493-501. doi: 10.1093/nar/25.8.1493.
The oncoprotein c-Myc plays an important role in cell proliferation, transformation, inhibition of differentiation and apoptosis. These functions most likely result from the transcription factor activity of c-Myc. As a heterodimer with Max, the c-Myc protein binds to the E-box sequence (CACGTG), which is also recognized by USF dimers. In order to test differences in target gene recognition of c-Myc/Max, Max and USF dimers, we compared the DNA binding characteristics of these proteins in vitro using vaccinia viruses expressing full-length c-Myc and Max proteins. As expected, purified c-Myc/max binds specifically to a consensus E-box. The optimal conditions for DNA binding by either c-Myc/Max, Max or USF dimers differ with respect to ionic strength and Mg2+ ion concentration. Most interestingly, the c-Myc/Max complex binds with a high affinity to its natural target, the rat ODC gene, which contains two adjacent, consensus E-boxes. High affinity binding results from teh ability of c-Myc/Max dimers to bind cooperatively to these E-boxes. We propose that differential cooperative binding by E-box binding transcription factors could contribute to target gene specificity.
癌蛋白c-Myc在细胞增殖、转化、抑制分化和凋亡过程中发挥着重要作用。这些功能很可能源于c-Myc的转录因子活性。作为与Max形成的异源二聚体，c-Myc蛋白与E盒序列（CACGTG）结合，该序列也能被USF二聚体识别。为了测试c-Myc/Max、Max和USF二聚体在靶基因识别上的差异，我们利用表达全长c-Myc和Max蛋白的痘苗病毒在体外比较了这些蛋白质的DNA结合特性。正如预期的那样，纯化的c-Myc/max特异性结合到共有E盒上。c-Myc/Max、Max或USF二聚体结合DNA的最佳条件在离子强度和Mg2+离子浓度方面有所不同。最有趣的是，c-Myc/Max复合物与其天然靶标大鼠ODC基因具有高亲和力，该基因包含两个相邻的共有E盒。高亲和力结合源于c-Myc/Max二聚体协同结合这些E盒的能力。我们提出，E盒结合转录因子的差异协同结合可能有助于靶基因特异性。
