Yeast Snf5p, a component of the Snf/Swi
complex, is evolutionarily conserved with homologs in S.
cerevisiae , S. pombe , C. elegans , D.
melanogaster , and human. The Snf/Swi proteins are required for
transcription of a variety of differently regulated genes, and genetic
and biochemical studies indicate that Snf/Swi remodels chromatin in an
ATP-dependent manner. Deletion analysis reveals an internal region of
Snf5p necessary for function. This region is conserved among all Snf5p
homologs and contains sequences required for activation and two
imperfect direct repeats. In a genetic screen for temperature-sensitive
alleles of SNF5 that affect growth on raffinose, two substitution
mutations were isolated that map to this domain, D475N and E582K. The
corresponding mutations made in SFH1 , the essential yeast
SNF5 homolog, also confer a Ts - phenotype, suggesting
conservation of an important function. Gel filtration analysis shows
that the Snf/Swi complex fails to assemble in the E582K mutant, even at
the permissive temperature (30°C). In contrast, Snf/Swi is intact in the
D475N mutant. Primer-extension analysis of the MNase-cleaved chromatin
of the SUC2 promoter in the mutants grown at 37°C indicates that
both mutations are incapable of inducing the chromatin changes seen
either in wild-type or in the D475N mutant at 30°C. These data provide
the first evidence that Snf5p plays an important role in both the
assembly and chromatin remodeling activity of the Snf/Swi complex.
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