Mechanism of regulatory target selection by the SOX high-mobility-group domain proteins as revealed by comparison of SOX1/2/3 and SOX9.
SOX proteins bind similar DNA motifs through their high-mobility-group (HMG) domains, but their action is highly specific with respect to target genes and cell type. We investigated the mechanism of target selection by comparing SOX1/2/3, which activate delta-crystallin minimal enhancer DC5, with SOX9, which activates Col2a1 minimal enhancer COL2C2. These enhancers depend on both the SOX binding site and the binding site of a putative partner factor. The DC5 site was equally bound and bent by the HMG domains of SOX1/2 and SOX9. The activation domains of these SOX proteins mapped at the distal portions of the C-terminal domains were not cell specific and were independent of the partner factor. Chimeric proteins produced between SOX1 and SOX9 showed that to activate the DC5 enhancer, the C-terminal domain must be that of SOX1, although the HMG domains were replaceable. The SOX2-VP16 fusion protein, in which the activation domain of SOX2 was replaced by that of VP16, activated the DC5 enhancer still in a partner factor-dependent manner. The results argue that the proximal portion of the C-terminal domain of SOX1/2 specifically interacts with the partner factor, and this interaction determines the specificity of the SOX1/2 action. Essentially the same results were obtained in the converse experiments in which COL2C2 activation by SOX9 was analyzed, except that specificity of SOX9-partner factor interaction also involved the SOX9 HMG domain. The highly selective SOX-partner factor interactions presumably stabilize the DNA binding of the SOX proteins and provide the mechanism for regulatory target selection.
Kamachi
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Institute for Molecular and Cellular Biology, Osaka University, Osaka 565-0871, Japan.
Cheah
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KS
Kondoh
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D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002642:Chick Embryo; D003094:Collagen / Q000235:genetics; D003459:Crystallins / Q000235:genetics; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D024002:HMGB Proteins; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics / Q000378:metabolism; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D055758:SOX9 Transcription Factor; D055748:SOXB1 Transcription Factors; D055751:SOXC Transcription Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D003459:Crystallins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D024002:HMGB Proteins; D017405:Herpes Simplex Virus Protein Vmw65; D006609:High Mobility Group Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; C490906:SOX1 protein, human; D055758:SOX9 Transcription Factor; D055748:SOXB1 Transcription Factors; D055751:SOXC Transcription Factors; C490793:Sox11 protein, mouse; C527783:Sox2 protein, mouse; C527786:Sox3 protein, mouse; C527933:Sox9 protein, mouse; D014157:Transcription Factors; D003094:Collagen