A central role for a single c-Myb binding site in a thymic locus control region.

Ess KC, Whitaker TL, Cost GJ, Witte DP, Hutton JJ, Aronow BJ
Mol Cell Biol. 1995 15 (10): 5707-15

PMID: 7565722 · PMCID: PMC230821 · DOI:10.1128/mcb.15.10.5707

Locus control regions (LCRs) are powerful assemblies of cis elements that organize the actions of cell-type-specific trans-acting factors. A 2.3-kb LCR in the human adenosine deaminase (ADA) gene first intron, which controls expression in thymocytes, is composed of a 200-bp enhancer domain and extended flanking sequences that facilitate activation from within chromatin. Prior analyses have demonstrated that the enhancer contains a 28-bp core region and local adjacent augmentative cis elements. We now show that the core contains a single critical c-Myb binding site. In both transiently cotransfected human cells and stable chromatin-integrated yeast cells, c-Myb strongly transactivated reporter constructs that contained polymerized core sequences. c-Myb protein was strongly evident in T lymphoblasts in which the enhancer was active and was localized within discrete nuclear structures. Fetal murine thymus exhibited a striking concordance of endogenous c-myb expression with that of mouse ADA and human ADA LCR-directed transgene expression. Point mutation of the c-Myb site within the intact 2.3-kb LCR severely attenuated enhancer activity in transfections and LCR activity in transgenic thymocytes. Within the context of a complex enhancer and LCR, c-Myb can act as an organizer of thymocyte-specific gene expression via a single binding site.

MeSH Terms (20)

Adenosine Deaminase Animals Base Sequence Binding Sites Cell Line Chromatin Enhancer Elements, Genetic Gene Expression Regulation, Developmental Humans Introns Mice Mice, Transgenic Molecular Sequence Data Point Mutation Proto-Oncogene Proteins Proto-Oncogene Proteins c-myb Saccharomyces cerevisiae T-Lymphocytes Thymus Gland Trans-Activators

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