Benezra R, Davis R L, Lockshon D, Turner D L, Weintraub H
Department of Genetics, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
Cell. 1990 Apr 6;61(1):49-59. doi: 10.1016/0092-8674(90)90214-y.
We have isolated a cDNA clone encoding a novel helix-loop-helix (HLH) protein, Id. Id is missing the basic region adjacent to the HLH domain that is essential for specific DNA binding in another HLH protein, MyoD. An in vitro translation product of Id can associate specifically with at least three HLH proteins (MyoD, E12, and E47) and attenuate their ability to bind DNA as homodimeric or heterodimeric complexes. Id is expressed at varying levels in all cell lines tested. In three cell lines that can be induced to undergo terminal differentiation, Id RNA levels decrease upon induction. Transfection experiments indicate that over-expression of Id inhibits the trans-activation of the muscle creatine kinase enhancer by MyoD. Based on these findings, we propose that HLH proteins lacking a basic region may negatively regulate other HLH proteins through the formation of nonfunctional heterodimeric complexes.
我们分离出了一个编码新型螺旋-环-螺旋（HLH）蛋白Id的cDNA克隆。Id缺少与HLH结构域相邻的碱性区域，而该区域对于另一种HLH蛋白MyoD的特异性DNA结合至关重要。Id的体外翻译产物可与至少三种HLH蛋白（MyoD、E12和E47）特异性结合，并减弱它们作为同二聚体或异二聚体复合物结合DNA的能力。Id在所测试的所有细胞系中均有不同水平的表达。在三种可诱导发生终末分化的细胞系中，诱导后Id RNA水平降低。转染实验表明，Id的过表达抑制了MyoD对肌肉肌酸激酶增强子的反式激活。基于这些发现，我们提出，缺乏碱性区域的HLH蛋白可能通过形成无功能的异二聚体复合物对其他HLH蛋白进行负调控。
