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Molecular and Cellular Biology, January 2001, p. 16-25, Vol. 21, No. 1
Instituto de Biología Molecular y
Celular de Plantas, Universidad Politécnica de Valencia-CSIC,
46022 Valencia, Spain
Received 10 July 2000/Returned for modification 30 August
2000/Accepted 6 October 2000
In the transcriptional response of Saccharomyces
cerevisiae to stress, both activators and repressors are
implicated. Here we demonstrate that the ion homeostasis determinant,
HAL1, is regulated by two antagonistically operating bZIP
transcription factors, the Sko1p repressor and the Gcn4p activator. A
single CRE-like sequence (CREHAL1) at position
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.16-25.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
The Sko1p Repressor and Gcn4p Activator
Antagonistically Modulate Stress-Regulated Transcription in
Saccharomyces cerevisiae
222 to
215 with the palindromic core sequence TTACGTAA
is essential for stress-induced expression of HAL1.
Down-regulation of HAL1 under normal growth conditions
requires specific binding of Sko1p to CREHAL1 and the corepressor gene SSN6. Release from this repression
depends on the function of the high-osmolarity glycerol pathway. The
Gcn4p transcriptional activator binds in vitro to the same
CREHAL1 and is necessary for up-regulated
HAL1 expression in vivo, indicating a dual control
mechanism by a repressor-activator pair occupying the same promoter
target sequence. gcn4 mutants display a strong sensitivity
to elevated K+ or Na+ concentrations in the
growth medium. In addition to reduced HAL1 expression, this
sensitivity is explained by the fact that amino acid uptake is
drastically impaired by high Na+ and K+
concentrations in wild-type yeast cells. The reduced amino acid biosynthesis of gcn4 mutants would result in amino acid
deprivation. Together with the induction of HAL1 by amino
acid starvation, these results suggest that salt stress and amino acid
availability are physiologically interconnected.
*
Corresponding author. Mailing address: Instituto de
Biología Molecular y Celular de Plantas, Universidad
Politécnica de Valencia-CSIC, Camino de Vera s/n, 46022 Valencia,
Spain. Phone: 34-96-3877860. Fax: 34-96-3877859. E-mail:
mproft{at}ibmcp.upv.es.
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