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Proc Natl Acad Sci U S A. 1990 Aug;87(15):5623-7.

MyoD binds cooperatively to two sites in a target enhancer sequence: occupancy of two sites is required for activation.

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1
Fred Hutchinson Cancer Research Center, Seattle, WA 98104.

Abstract

MyoD is a master regulatory gene for myogenesis. Its product, the MyoD protein, appears to act by binding to muscle-specific enhancer sequences. We show that MyoD binds cooperatively to two sites in the muscle-specific creatine kinase enhancer; this is dramatically reflected in dissociation-rate measurements. A deletion of the acidic N terminus (residues 3-56) results in a protein that binds normally to single sites but fails to bind cooperatively to two adjacent sites, suggesting a role of the N terminus in cooperative interactions. In transfection assays, a reporter gene flanked by a single MyoD binding site fails to be activated by cotransfected MyoD expression vectors. In contrast, a reporter with two or more MyoD binding sites is activated by wild-type MyoD but not by N-terminally deleted MyoD. A reporter gene with a single binding site, although not activated by MyoD, can nonetheless compete for expression with a reporter gene containing three sites. Thus, in vivo, a single site can bind MyoD, but occupancy of two or more sites is required for subsequent transcriptional activation.

PMID:
2377600
PMCID:
PMC54379
[Indexed for MEDLINE]
Free PMC Article
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