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Molecular and Cellular Biology, May 2000, p. 3027-3036, Vol. 20, No. 9
Department of Biomolecular Chemistry,
University of Wisconsin
Received 19 August 1999/Returned for modification 11 October
1999/Accepted 4 February 2000
In addition to its roles in translocation of preproteins across
membranes, Ydj1 facilitates the maturation of Hsp90 substrates, including mammalian steroid receptors, which activate transcription in
yeast in a hormone-dependent manner. To better understand Ydj1's function, we have constructed and analyzed an array of Ydj1 mutants in
vivo. Both the glucocorticoid receptor and the estrogen receptor exhibited elevated activity in the absence of hormone in all
ydj1 mutant strains, indicating a strict requirement for
Ydj1 activity in hormonal control. Glucocorticoid receptor containing a
mutation in the carboxy-terminal transcriptional activation domain,
AF-2, retained elevated basal activity, while mutation of the
amino-terminal transactivation domain, AF-1, eliminated the elevated
basal activity observed in ydj1 mutant strains. This result
indicates that the source of activity is AF-1, which is normally
repressed by the carboxy-terminal hormone binding domain in the absence
of hormone. Chimeric proteins containing the hormone binding domain of
the estrogen or glucocorticoid receptor fused to heterologous
activation and DNA binding domains also exhibited elevated activity in
the absence of hormone. Thus, Ydj1 mutants appear to increase basal receptor activity by altering the ability of the hormone binding domain
of the receptor to repress nearby activation domains. We propose that
Ydj1 functions to present steroid receptors to the Hsp90 pathway for
folding and hormonal control. In the presence of Ydj1 mutants that fail
to bind substrate efficiently, some receptor escapes the Hsp90 pathway,
resulting in constitutive activity.
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Copyright © 2000, American Society for Microbiology. All rights reserved.
A Role for the Hsp40 Ydj1 in Repression of Basal
Steroid Receptor Activity in Yeast
Madison, Madison, Wisconsin 53706
*
Corresponding author. Mailing address: 1300 University
Ave., Department of Biomolecular Chemistry, University of
Wisconsin
Madison, Madison, WI 53706. Phone: (608) 263-7105. Fax:
(608) 262-5253. E-mail: ecraig{at}facstaff.wisc.edu.
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