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Journal of Bacteriology, September 2001, p. 4950-4957, Vol. 183, No. 17
Department of Biology, Indiana
University-Purdue University at Indianapolis, Indianapolis, Indiana
46202,1 and Institute of Human
Nutrition2 and Department of
Pediatrics,3 Columbia University College of
Physicians and Surgeons, New York, New York 10032
Received 16 April 2001/Accepted 14 June 2001
Saccharomyces cerevisiae transcribes two genes,
ARE1 and ARE2, that contribute
disproportionately to the esterification of sterols. Are2p is the major
enzyme isoform in a wild-type cell growing aerobically. This likely
results from a combination of differential transcription initiation and
transcript stability. By using ARE1 and
ARE2 promoter fusions to lacZ reporters,
we demonstrated that transcriptional initiation from the
ARE1 promoter is significantly reduced compared to that
from the ARE2 promoter. Furthermore, the half-life of
the ARE2 mRNA is approximately 12 times as long as that
of the ARE1 transcript. We present evidence that the
primary role of the minor sterol esterification isoform encoded by
ARE1 is to esterify sterol intermediates, whereas the role of the ARE2 enzyme is to esterify ergosterol, the
end product of the pathway. Accordingly, the ARE1
promoter is upregulated in strains that accumulate ergosterol
precursors. Furthermore, ARE1 and ARE2
are oppositely regulated by heme. Under heme-deficient growth
conditions, ARE1 was upregulated fivefold while
ARE2 was down-regulated. ARE2 requires
the HAP1 transcription factor for optimal expression,
and both ARE genes are derepressed in a
rox1 (repressor of oxygen) mutant genetic background. We
further report that the ARE genes are not subject to end
product inhibition; neither ARE1 nor ARE2
transcription is altered in an are mutant background,
nor does overexpression of either ARE gene alter the response of the ARE-lacZ reporter constructs. Our
observations are consistent with an important physiological role for
Are1p during anaerobic growth when heme is limiting and sterol
precursors may accumulate. Conversely, Are2p is optimally required
during aerobiosis when ergosterol is plentiful.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.17.4950-4957.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Transcriptional Regulation of the Two Sterol
Esterification Genes in the Yeast Saccharomyces
cerevisiae

*
Corresponding author. Mailing address for M. Bard:
IUPUI Biology Department, 723 W. Michigan St., Indianapolis, IN 46202. Phone: (317) 274-0593. Fax: (317) 274-2846. E-mail:
mbard{at}iupui.edu. Mailing address for S. L. Sturley:
Institute of Human Nutrition, Columbia University College of Physicians
and Surgeons, 650 W. 168th St., New York, NY 10032. Phone: (212)
305-6304. (Fax): (212) 305-3079. E-mail: sls37{at}columbia.edu.
Present address: Cardiovascular Division, Department of Medicine,
Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115.
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