A Specific Isoform of hnRNP D Interacts with DNA in the LR1 Heterodimer: Canonical RNA Binding Motifs in a Sequence-specific Duplex DNA Binding Protein*
- From the Departments of ‡Molecular Biophysics and Biochemistry and ‖Genetics, Yale University, New Haven, Connecticut 06520-8114
Abstract
The B cell-specific, sequence-specific duplex DNA-binding protein LR1 is a transcriptional activator and may also function in heavy chain class switch recombination. LR1 is composed of two polypeptides, a 106-kDa subunit that is nucleolin, and a 45-kDa subunit that we now show to be a specific isoform of hnRNP D. hnRNP D and nucleolin both contain canonical RNA binding domains (RBDs also called RRMs) and Arg-Gly-Gly (RGG) motifs. Although these motifs are not commonly associated with sequence-specific recognition of duplex DNA, nonetheless LR1 binds duplex DNA with high affinity (K D = 1.8 nm) and clear sequence specificity. Two RBD-RGG proteins can therefore combine to produce a sequence-specific duplex DNA-binding protein.
Footnotes
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↵* This research was supported by National Institutes of Health Grant R01 GM39799 (to N. M.), by National Research Service Award GM15948 (to L. A. D.), and by a postdoctoral fellowship from Genetics Training Program T32 CA09159 (to L. A. H.).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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↵§ These authors contributed equally to this work.
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↵¶ Present address: Dept. of Experimental Surgery, Mayo Foundation, Rochester, MN 55905.
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↵** To whom correspondence should be addressed: Dept. of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Ave., New Haven, CT 06520-8114. Tel.: 203-432-5641; Fax: 203-432-3047; E-mail:nancy.maizels{at}yale.edu.
- Abbreviations:
- hnRNP D
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heterogeneous nuclear ribonucleoprotein D
- RBD
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RNA binding domain
- DTT
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dithiothreitol
- MBP
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maltose-binding protein.
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- Received June 16, 1998.
- Revision received July 7, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
