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Molecular and Cellular Biology, June 1999, p. 4324-4333, Vol. 19, No. 6
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
A New Class of Repression Modules Is Critical for
Heme Regulation of the Yeast Transcriptional Activator Hap1
Angela
Hach,
Thomas
Hon, and
Li
Zhang*
Department of Biochemistry, NYU Medical
Center, New York, New York 10016
Received 18 December 1998/Returned for modification 8 February
1999/Accepted 24 March 1999
Heme plays key regulatory roles in numerous molecular and cellular
processes for systems that sense or use oxygen. In the yeast
Saccharomyces cerevisiae, oxygen sensing and heme signaling are mediated by heme activator protein 1 (Hap1). Hap1 contains seven
heme-responsive motifs (HRMs): six are clustered in the heme domain,
and a seventh is near the activation domain. To determine the
functional role of HRMs and to define which parts of Hap1 mediate heme
regulation, we carried out a systematic analysis of Hap1 mutants with
various regions deleted or mutated. Strikingly, the data show that HRM1
to -6, located in the previously designated Hap1 heme domain, have
little impact on heme regulation. All seven HRMs are dispensable for
Hap1 repression in the absence of heme, but HRM7 is required for Hap1
activation by heme. More importantly, we show that a novel class of
repression modules
RPM1, encompassing residues 245 to 278; RPM2,
encompassing residues 1061 to 1185; and RPM3, encompassing residues 203 to 244
is critical for Hap1 repression in the absence of heme.
Biochemical analysis indicates that RPMs mediate Hap1 repression, at
least partly, by the formation of a previously identified higher-order
complex termed the high-molecular-weight complex (HMC), while HRMs
mediate heme activation by permitting heme binding and the disassembly
of the HMC. These findings provide significant new insights into the
molecular interactions critical for Hap1 repression in the absence of
heme and Hap1 activation by heme.
*
Corresponding author. Mailing address: Department of
Biochemistry, NYU Medical Center, 550 First Ave., New York, NY 10016. Phone: (212) 263-8506. Fax: (212) 263-8166. E-mail:
zhang102{at}mcrcr0.med.nyu.edu.
Molecular and Cellular Biology, June 1999, p. 4324-4333, Vol. 19, No. 6
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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