Blackwood E M, Eisenman R N
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98104.
Science. 1991 Mar 8;251(4998):1211-7. doi: 10.1126/science.2006410.
The myc protooncogene family has been implicated in cell proliferation, differentiation, and neoplasia, but its mechanism of function at the molecular level is unknown. The carboxyl terminus of Myc family proteins contains a basic region helix-loop-helix leucine zipper motif (bHLH-Zip), which has DNA-binding activity and has been predicted to mediate protein-protein interactions. The bHLH-Zip region of c-Myc was used to screen a complementary DNA (cDNA) expression library, and a bHLH-Zip protein, termed Max, was identified. Max specifically associated with c-Myc, N-Myc, and L-Myc proteins, but not with a number of other bHLH, bZip, or bHLH-Zip proteins. The interaction between Max and c-Myc was dependent on the integrity of the c-Myc HLH-Zip domain, but not on the basic region or other sequences outside the domain. Furthermore, the Myc-Max complex bound to DNA in a sequence-specific manner under conditions where neither Max nor Myc exhibited appreciable binding. The DNA-binding activity of the complex was dependent on both the dimerization domain and the basic region of c-Myc. These results suggest that Myc family proteins undergo a restricted set of interactions in the cell and may belong to the more general class of eukaryotic DNA-binding transcription factors.
myc原癌基因家族与细胞增殖、分化及肿瘤形成有关，但其在分子水平的功能机制尚不清楚。Myc家族蛋白的羧基末端包含一个碱性区域螺旋-环-螺旋亮氨酸拉链基序（bHLH-Zip），该基序具有DNA结合活性，并被预测可介导蛋白质-蛋白质相互作用。利用c-Myc的bHLH-Zip区域筛选互补DNA（cDNA）表达文库，鉴定出一种名为Max的bHLH-Zip蛋白。Max特异性地与c-Myc、N-Myc和L-Myc蛋白结合，但不与许多其他bHLH、bZip或bHLH-Zip蛋白结合。Max与c-Myc之间的相互作用依赖于c-Myc HLH-Zip结构域的完整性，而不依赖于该结构域之外的碱性区域或其他序列。此外，在Max和Myc均未表现出明显结合的条件下，Myc-Max复合物以序列特异性方式结合DNA。该复合物的DNA结合活性依赖于c-Myc的二聚化结构域和碱性区域。这些结果表明，Myc家族蛋白在细胞内经历了一组有限的相互作用，可能属于更广泛的真核DNA结合转录因子类别。
