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Molecular and Cellular Biology, December 1999, p. 8123-8135, Vol. 19, No. 12
Department of Biology and Center for
Molecular Genetics, University of California, San Diego, La Jolla,
California 92093-0347
Received 21 July 1999/Returned for modification 2 September
1999/Accepted 9 September 1999
To investigate the mechanisms of transcriptional enhancement by the
p300 coactivator, we analyzed wild-type and mutant versions of p300
with a chromatin transcription system in vitro. Estrogen receptor,
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Copyright © 1999, American Society for Microbiology. All rights reserved.
Biochemical Analysis of Distinct Activation
Functions in p300 That Enhance Transcription Initiation with
Chromatin Templates

B p65 plus Sp1, and Gal4-VP16 were used as different sequence-specific activators. The CH3 domain (or E1A-binding region) was found to be essential for the function of each of the activators tested. The bromodomain was also observed to be generally important for
p300 coactivator activity, though to a lesser extent than the CH3
domain/E1A-binding region. The acetyltransferase activity and the
C-terminal region (containing the steroid receptor
coactivator/p160-binding region and the glutamine-rich region) were
each found to be important for activation by estrogen receptor but not
for that by Gal4-VP16. The N-terminal region of p300, which had been
previously found to interact with nuclear hormone receptors, was not
seen to be required for any of the activators, including estrogen
receptor. Single-round transcription experiments revealed that the
functionally important subregions of p300 contribute to its ability to
promote the assembly of transcription initiation complexes. In
addition, the acetyltransferase activity of p300 was observed to be
distinct from the broadly essential activation function of the CH3
domain/E1A-binding region. These results indicate that specific regions
of p300 possess distinct activation functions that are differentially
required to enhance the assembly of transcription initiation complexes. Interestingly, with the estrogen receptor, four distinct regions of
p300 each have an essential role in the transcription activation process. These data exemplify a situation in which a network of multiple activation functions is required to achieve gene transcription.
*
Corresponding author. Mailing address: Department of
Biology, 0347, Pacific Hall, Room 2212B, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0347. Phone: (858) 534-4608. Fax: (858) 534-0555. E-mail: jkadonaga{at}ucsd.edu.
Present address: Department of Molecular Biology and Genetics,
Cornell University, Ithaca, NY 14853.
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