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Mol. Cell. Biol., Sep 1995, 4890-4897, Vol 15, No. 9
JT Halladay and EA Craig
Strains carrying deletions in both the SSA1 and SSA2 HSP70 genes of
Saccharomyces cerevisiae exhibit pleiotropic phenotypes, including the
inability to grow at 37 degrees C or higher, reduced growth rate at
permissive temperatures, increased HSP gene expression, and constitutive
thermotolerance. A screen for extragenic suppressors of the ssa1 ssa2
slow-growth phenotype identified a spontaneous dominant suppressor
mutation, EXA3-1 (R.J. Nelson, M. Heschl, and E.A. Craig, Genetics
131:277-285, 1992). Here we report that EXA3-1 is an allele of HSF1, which
encodes the heat shock transcription factor (HSF). Strains containing the
EXA3-1 allele in a wild-type background exhibit a 10- to 15-fold reduction
in HSF activity during steady-state growth conditions as well as a delay in
the accumulation of the SSA4, HSP26, and HSP104 mRNAs after a heat shock.
EXA3-1-mediated suppression is the result of a single amino acid
substitution of a highly conserved residue in the HSF DNA-binding domain
which drastically reduces the ability of HSF to bind to heat shock elements
as evaluated by band shift analysis. Together, these results indicate that
the poor growth of ssa1 ssa2 strains is the result, at least in part, of
the overproduction of a deleterious heat shock protein(s). This conclusion
is supported by the fact that the levels of at least some heat shock
proteins are reduced in ssa1 ssa2 cells containing the EXA3-1
allele.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
A heat shock transcription factor with reduced activity suppresses a yeast HSP70 mutant
Department of Biomolecular Chemistry, University of Wisconsin, Madison 53706, USA.
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