Intramolecular regulation of MyoD activation domain conformation and function.
The MyoD family of basic helix-loop-helix (bHLH) proteins is required for myogenic determination and differentiation. The basic region carries the myogenic code and DNA binding specificity, while the N terminus contains a potent transcriptional activation domain. Myogenic activation is abolished when the basic region, bound to a myogenic E box, carries a mutation of Ala-114. It has been proposed that DNA binding of the MyoD basic region leads to recruitment of a recognition factor that unmasks the activation domain. Here we demonstrate that an A114N mutant exhibits an altered conformation in the basic region and that this local conformational difference can lead to a more global change affecting the conformation of the activation domain. This suggests that the deleterious effects of this class of mutations may result directly from defective conformation. Thus, the activation domain is unmasked only upon DNA binding by the correct basic region. Such a coupled conformational relationship may have evolved to restrict myogenic specificity to a small number of bHLH proteins among many with diverse functions yet with DNA binding specificities known to be similar.
Institute for Genetic Medicine and Department of Biochemistry and Molecular Biology, University of Southern California School of Medicine, Los Angeles, California 90033, USA.
J
J
Huang
H
H
Weintraub
L
L
Kedes
D000409:Alanine; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017570:MyoD Protein / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D004268:DNA-Binding Proteins; D017570:MyoD Protein; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D000409:Alanine