Tonissen K F, Krieg P A
Department of Zoology, University of Texas at Austin 78712.
Oncogene. 1994 Jan;9(1):33-8.
Max is a small helix-loop-helix protein which forms heterodimers with members of the Myc protein family. Myc/Max heterodimers exhibit sequence-specific DNA binding with much greater affinity than Myc homodimers. The Xenopus laevis homologue of Max, XMax, is shorter than the equivalent mammalian protein. This difference results from the deletion of a 24 amino acid sequence located near the C-terminus of the protein. Xenopus max transcripts undergo alternative splicing. In addition to the 27 base alternatively spliced sequence (exon A) previously detected in mice and humans, some Xmax transcripts also contain an 81 base sequence (exon B) at a second site within the coding sequence. Although exon B insertion alters part of the leucine zipper protein/protein interaction domain, the resulting XMax protein retains the ability to form stable heterodimers with both c-Myc and N-Myc. Xmax mRNA is present at approximately constant levels during early development. This contrasts with the rapidly changing levels of c-myc and N-myc mRNA in the embryo and has implications for regulation of gene expression during differentiation. All four alternatively spliced forms of Xmax mRNA are present during development and in all adult tissue examined.
Max是一种小的螺旋-环-螺旋蛋白，它与Myc蛋白家族的成员形成异源二聚体。Myc/Max异源二聚体表现出序列特异性DNA结合，其亲和力远高于Myc同源二聚体。非洲爪蟾Max的同源物XMax比相应的哺乳动物蛋白短。这种差异是由于蛋白质C末端附近一个24个氨基酸序列的缺失导致的。非洲爪蟾max转录本会发生可变剪接。除了之前在小鼠和人类中检测到的27个碱基的可变剪接序列（外显子A）外，一些Xmax转录本在编码序列内的第二个位点还包含一个81个碱基的序列（外显子B）。尽管外显子B的插入改变了亮氨酸拉链蛋白/蛋白相互作用结构域的一部分，但产生的XMax蛋白仍保留了与c-Myc和N-Myc形成稳定异源二聚体的能力。Xmax mRNA在早期发育过程中水平大致恒定。这与胚胎中c-myc和N-myc mRNA水平的快速变化形成对比，并且对分化过程中的基因表达调控具有重要意义。Xmax mRNA的所有四种可变剪接形式在发育过程中和所有检测的成年组织中均存在。
