A number of
studies previously suggested that the Snf/Swi complex of S.
cerevisiae remodels nucleosomes to help transcription factors bind
to their sites. We have taken three different strategies to learn about
Snf/Swi function in vivo . First, to determine how many genes
require Snf/Swi for normal transcription, we have used DNA microarrays
to study the effect of snf/swi null mutations on mRNA levels of
the entire yeast genome. Less than three percent of all mRNAs are
altered by at least three-fold. While most affected mRNAs decrease in
level, some mRNAs show increases. In addition, cells grown in rich media
show a different pattern than cells grown in minimal media. Second, we
have examined if the transcription of one Snf/Swi-dependent gene,
SUC2 , is also controlled by the histone acetyltransferase Gcn5.
Previous genetic evidence suggested that Snf/Swi and Gcn5 may be
partially redundant for transcriptional activation. Our results have
shown that in the absence of either function, SUC2 mRNA levels
are greatly reduced, well below that found in either single mutant.
Finally, we have studied the requirement for Snf/Swi in the
establishment and maintenance of SUC2 transcription. Our studies
suggest that Snf/Swi is required for both establishment and maintenance
of a fully active SUC2 promoter. In summary, the requirement for
Snf/Swi occurs at a number of promoters in vivo and its role in
overcoming repression by nucleosomes is at least partially redundant
with that of Gcn5.
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