Tissue-specific gene activation by MyoD: determination of specificity by cis-acting repression elements.
MyoD is a muscle-specific transcriptional activator; E12 is a B-cell activator. An IgH enhancer is activated almost 100-fold by E12 but not at all by Myo; an MCK enhancer is activated almost 1000-fold by MyoD and not at all by E12. MyoD and E12 are both basic helix-loop-helix proteins that bind to similar E-box sequences (CANNTG); the IgH enhancer contains the same E boxes as the MCK enhancer, yet each retains exclusive specificity for either E12 or MyoD, respectively. We show that the IgH enhancer contains a cis-acting negative element that is directed at MyoD, but not at E12. This repression requires the mu E5 E box within the IgH enhancer; however, the specificity for repression, as opposed to activation, is associated with 2 bp flanking each side of the mu E5 E box. The target for repression of MyoD in the IgH enhancer is the bHLH region of MyoD. Our results suggest that MyoD only activates myogenic genes because nonmuscle enhancers that contain E boxes also contain negative elements that prevent MyoD activity.
Weintraub
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H
Hutchinson Cancer Center, Howard Hughes Medical Institute, Seattle, Washington 98104.
Genetta
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Kadesch
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D016475:3T3 Cells; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology; D001483:Base Sequence; D001665:Binding Sites; D003402:Creatine Kinase / Q000235:genetics; D004247:DNA / Q000235:genetics; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D018257:Helix-Loop-Helix Motifs; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000201:enzymology; D017570:MyoD Protein / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D014018:Tissue Distribution; D015533:Transcriptional Activation
D007143:Immunoglobulin Heavy Chains; D017570:MyoD Protein; D012097:Repressor Proteins; D004247:DNA; D003402:Creatine Kinase