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¹ Department of Immunobiology, Yale University Medical School, New Haven, CT 06520
² Laboratory of Molecular Immunology, National Heart, Lung, and Blood Institute/National Institutes of Health, Bethesda, MD 20892

CORRESPONDENCE Tian Chi: Tian.Chi{at}yale.edu

We have developed a general strategy for creating littermates bearing either a tissue-specific point mutation or deletion in any target gene, and used the method to dissect the roles of Brg, the ATPase subunit of the chromatin-remodeling Brg-associated factor (BAF) complex, in early thymocyte development. We found that a point mutation that inactivates the Brg ATPase recapitulates multiple defects previously described for Brg deletion (Chi, T.H., M. Wan, P.P. Lee, K. Akashi, D. Metzger, P. Chambon, C.B. Wilson, and G.R. Crabtree. 2003. Immunity. 19:169–182). However, the point mutant helps reveal unexpected roles of Brg in CD25 repression and CD4 activation. Surprisingly, CD4 activation occurs independently of the Brg ATPase and is perhaps mediated by physical interactions between Brg and the CD4 locus. Our study thus suggests that the BAF complex harbors novel activities that can be necessary and even sufficient for stimulating transcription from an endogenous chromatin template in the absence of Brg-dependent remodeling of that template. We conclude that conditional point mutants, rarely used in mammalian genetics, can help uncover important gene functions undetectable or overlooked in deletion mutants.

M. Wan, J. Zhang, and K. Cui contributed equally to this paper.

J. Zhang's present address is Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205.

© 2008 Jani et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jem.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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This article has been cited by other articles:

• Jani, A., Wan, M., Zhang, J., Cui, K., Wu, J., Preston-Hurlburt, P., Khatri, R., Zhao, K., Chi, T. (2008). A novel genetic strategy reveals unexpected roles of the Swi-Snf-like chromatin-remodeling BAF complex in thymocyte development. JCB 183: i7-i7 [Full Text]  

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