Interactions between LIM Domains and the LIM Domain-binding Protein Ldb1*
- From the ‡Laboratory of Molecular Genetics and‖Laboratory of Mammalian Genes and Development, NICHD, National Institutes of Health, Bethesda, Maryland 20892
Abstract
LIM domains mediate protein-protein interactions and, within LIM-homeodomain proteins, act as negative regulators of the transcriptional activation function of the protein. The recently described protein Ldb1 (also known as NLI; LIM domain-binding protein) binds LIM domains in vitro and synergizes with the LIM-homeodomain protein Xlim-1 in frog embryo microinjection experiments. In this study we localized the transcriptional activation domain of Xlim-1 to its carboxyl-terminal region, and characterized the interactions of the amino-terminally located LIM domains with Ldb1. Ldb1 binds LIM domains through its carboxyl-terminal region, and can form homodimers via its amino-terminal region. Optimal binding to Ldb1 required tandem LIM domains, while single domains could bind at lower but clearly measurable efficiency. In animal explant experiments, synergism of Ldb1 with Xlim-1 in the activation of downstream genes required both the region containing the dimerization domain of Ldb1 and the region containing the LIM-binding domain. The role of Ldb1 may be to recruit other transcriptional activators depending on the promoter context and LIM-homeodomain partner involved.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Contributed equally to the results of this work.
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↵¶ Supported by a National Research Council Research Associateship.
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↵** To whom correspondence should be addressed: Bldg. 6B, Rm. 413, Laboratory of Molecular Genetics, NICHD, NIH, Bethesda, MD 20892-2790. Tel.: 301-496-4448; Fax: 301-496-0243; E-mail: idawid{at}nih.gov.
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↵1 The abbreviations used are: Ldb, LIM domain-binding protein; NLI, nuclear LIM interactor; DBD, DNA-binding domain; AD, activation domain; PCR, polymerase chain reaction.
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- Received June 23, 1997.
- Revision received November 28, 1997.
- The American Society for Biochemistry and Molecular Biology, Inc.
