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Molecular and Cellular Biology, September 1999, p. 6441-6447, Vol. 19, No. 9
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Trithorax and ASH1 Interact Directly and Associate with the Trithorax Group-Responsive bxd Region of the Ultrabithorax Promoter

Tanya Rozovskaia,1 Sergei Tillib,2 Sheryl Smith,2 Yurii Sedkov,2 Orit Rozenblatt-Rosen,1 Svetlana Petruk,2 Takahiro Yano,2 Tatsuya Nakamura,2 Levana Ben-Simchon,1 John Gildea,3 Carlo M. Croce,2 Allen Shearn,3 Eli Canaani,1 and Alexander Mazo2,*

Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania2; Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel1; and Department of Biology, Johns Hopkins University, Baltimore, Maryland3

Received 20 April 1999/Returned for modification 25 May 1999/Accepted 17 June 1999

Trithorax (TRX) and ASH1 belong to the trithorax group (trxG) of transcriptional activator proteins, which maintains homeotic gene expression during Drosophila development. TRX and ASH1 are localized on chromosomes and share several homologous domains with other chromatin-associated proteins, including a highly conserved SET domain and PHD fingers. Based on genetic interactions between trx and ash1 and our previous observation that association of the TRX protein with polytene chromosomes is ash1 dependent, we investigated the possibility of a physical linkage between the two proteins. We found that the endogenous TRX and ASH1 proteins coimmunoprecipitate from embryonic extracts and colocalize on salivary gland polytene chromosomes. Furthermore, we demonstrated that TRX and ASH1 bind in vivo to a relatively small (4 kb) bxd subregion of the homeotic gene Ultrabithorax (Ubx), which contains several trx response elements. Analysis of the effects of ash1 mutations on the activity of this regulatory region indicates that it also contains ash1 response element(s). This suggests that ASH1 and TRX act on Ubx in relatively close proximity to each other. Finally, TRX and ASH1 appear to interact directly through their conserved SET domains, based on binding assays in vitro and in yeast and on coimmunoprecipitation assays with embryo extracts. Collectively, these results suggest that TRX and ASH1 are components that interact either within trxG protein complexes or between complexes that act in close proximity on regulatory DNA to maintain Ubx transcription.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Room 485, Jefferson Alumni Hall, 1020 Locust St., Philadelphia, PA 19107. Phone: (215) 503-4785. Fax: (215) 923-7144. E-mail: mazo{at}lac.jci.tju.edu.

Molecular and Cellular Biology, September 1999, p. 6441-6447, Vol. 19, No. 9
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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