Chromatin Remodeling Mediated by Drosophila GAGA Factor

Chromatin Remodeling Mediated by Drosophila GAGA Factor - M...

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Unformatted text preview: M OLECULAR AND CELLULAR BIOLOGY, 0270-7306/98/$04.00 1 May 1998, p. 2455–2461 Vol. 18, No. 5 Copyright © 1998, American Society for Microbiology Chromatin Remodeling Mediated by Drosophila GAGA Factor and ISWI Activates fushi tarazu Gene Transcription In Vitro MASAHIRO OKADA AND SUSUMU HIROSE* Department of Genetics, The Graduate University for Advanced Studies, and Department of Developmental Genetics, National Institute of Genetics, Mishima, Shizuoka-ken 411, Japan Received 30 December 1997/Returned for modification 6 February 1998/Accepted 24 February 1998 GAGA factor is known to remodel the chromatin structure in concert with nucleosome-remodeling factor NURF in a Drosophila embryonic S150 extract. The promoter region of the Drosophila fushi tarazu ( ftz ) gene carries several binding sites for GAGA factor. Both the GAGA factor-binding sites and GAGA factor per se are necessary for the proper expression of ftz in vivo. We observed transcriptional activation of the ftz gene when a preassembled chromatin template was incubated with GAGA factor and the S150 extract. The chromatin structure within the ftz promoter was specifically disrupted by incubation of the preassembled chromatin with GAGA factor and the S150 extract. Both transcriptional activation and chromatin disruption were blocked by an antiserum raised against ISWI or by base substitutions in the GAGA factor-binding sites in the ftz promoter region. These results demonstrate that GAGA factor- and ISWI-mediated disruption of the chromatin struc- ture within the promoter region of ftz activates transcription on the chromatin template. Chromatin structure appears to play a key role in the regu- lation of gene expression in eukaryotes (12, 13, 34, 44). Since chromatin structure represses transcription by preventing the binding of transcriptional regulators and transcription machin- ery to their target sequences, some mechanisms such as chro- matin remodeling likely counteract this repressive effect (7, 17, 21). Indeed, transcriptional activation usually accompanies re- modeling of chromatin. For example, the promoter region of the yeast PHO5 gene is covered by nucleosomes, but the or- dered array of nucleosomes disappears from the promoter upon induction of the gene by phosphate starvation (1). Trans- activation by certain regulators requires recruitment of histone acetyltransferase through coactivators (4, 25, 26, 46). The relationship between chromatin structure and transcrip- tion was also studied in vitro. The affinity of TATA-binding protein for the TATA element is significantly reduced when the TATA element is covered by a nucleosome (17). It was shown that the binding of TFIID to the TATA element prior to chromatin assembly alleviates the nucleosome-mediated re- pression of transcription (45). These observations suggested that remodeling of the chromatin structure around the pro- moter is crucial for transcriptional activation on the chromatin template. Pazin et al. reported the NF-template....
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Chromatin Remodeling Mediated by Drosophila GAGA Factor - M...

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