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Molecular and Cellular Biology, January 2000, p. 634-647, Vol. 20, No. 2
The Wistar Institute, Philadelphia,
Pennsylvania 19104,1 and Johns Hopkins
University, Baltimore, Maryland 212052
Received 3 August 1999/Returned for modification 5 October
1999/Accepted 13 October 1999
SAGA is a 1.8-MDa yeast protein complex that is composed of
several distinct classes of transcription-related factors, including the adaptor/acetyltransferase Gcn5, Spt proteins, and a subset of
TBP-associated factors. Our results indicate that mutations that
completely disrupt SAGA (deletions of SPT7 or
SPT20) strongly reduce transcriptional activation at the
HIS3 and TRP3 genes and that Gcn5 is required
for normal HIS3 transcriptional start site selection.
Surprisingly, mutations in Spt proteins involved in the SAGA-TBP
interaction (Spt3 and Spt8) cause derepression of HIS3 and
TRP3 transcription in the uninduced state. Consistent with
this finding, wild-type SAGA inhibits TBP binding to the HIS3 promoter in vitro, while SAGA lacking Spt3 or Spt8
is not inhibitory. We detected two distinct forms of SAGA in cell
extracts and, strikingly, one lacks Spt8. Conditions that induce
HIS3 and TRP3 transcription result in an
altered balance between these complexes strongly in favor of the form
without Spt8. These results suggest that the composition of SAGA
may be dynamic in vivo and may be regulated through dissociable
inhibitory subunits.
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Inhibition of TATA-Binding Protein Function by SAGA
Subunits Spt3 and Spt8 at Gcn4-Activated Promoters
*
Corresponding author. Mailing address: The Wistar
Institute, 3601 Spruce St., Room 389, Philadelphia, PA 19104. Phone:
(215) 898-3922. Fax: (215) 898-0663. E-mail:
berger{at}wista.wistar.upenn.edu.
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