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Mol Cell Biol, April 1998, p. 1774-1782, Vol. 18, No. 4
Molecular Genetics Program, Wadsworth Center,
New York State Department of Health, and State University of New
York School of Public Health, Albany, New York 12201-2002
Received 12 September 1997/Returned for modification 23 October
1997/Accepted 6 January 1998
The SWI-SNF complex in yeast and related complexes in higher
eukaryotes have been implicated in assisting gene activation by
overcoming the repressive effects of chromatin. We show that the
ability of the transcriptional activator GAL4 to bind to a site in a
positioned nucleosome is not appreciably impaired in swi
mutant yeast cells. However, chromatin remodeling that depends on a
transcriptional activation domain shows a considerable, although not
complete, SWI-SNF dependence, suggesting that the SWI-SNF complex
exerts its major effect at a step subsequent to activator binding. We
tested this idea further by comparing the SWI-SNF dependence of a
reporter gene based on the GAL10 promoter, which has an
accessible upstream activating sequence and a nucleosomal TATA element,
with that of a CYC1-lacZ reporter, which has a relatively accessible TATA element. We found that the GAL10-based
reporter gene showed a much stronger SWI-SNF dependence than did the
CYC1-lacZ reporter with several different activators.
Remarkably, transcription of the GAL10-based reporter by a
GAL4-GAL11 fusion protein showed a nearly complete requirement for the
SWI-SNF complex, strongly suggesting that SWI-SNF is needed to allow
access of TFIID or the RNA polymerase II holoenzyme. Taken together,
our results demonstrate that chromatin remodeling in vivo can occur by
both SWI-SNF-dependent and -independent avenues and suggest that the SWI-SNF complex exerts its major effect in transcriptional activation at a step subsequent to transcriptional activator-promoter recognition.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
SWI-SNF Complex Participation in Transcriptional
Activation at a Step Subsequent to Activator Binding
*
Corresponding author. Mailing address: Wadsworth
Center, Albany, NY 12201-2002. Phone: (518) 486-3116. Fax: (518)
474-3181. E-mail: Randall.Morse{at}wadsworth.org.
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