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novel HATs OFF compounds. Yeast is, in fact, an ideal
system, which couples to the evolutionary conservation of
the fundamental mechanisms of gene regulation the pecu-
liar use of a variety of single gene disrupted and mutant
strains that can be easily tested in comparison with the
respective wild-type isogenic background. The search for
Gcn5p inhibitors capable of reproducing slow growth in
gcn5D was what initially motivated us to assay novel, small
molecules in yeast. Here, we provide evidence for an
inhibitory effect the cell-permeable MC1626 specifically
exerted on wild type cells. Inhibition was significantly
diminished in a null gcn5D and a HAT catalytic mutant
strain (F221A). This result was obtained in different strain
backgrounds, proving that in the absence of Gcn5p the
main target of the inhibitor alternative pathways may
override the absence of Gcn5p. We also have demonstrated
that MC1626 inhibited Gcn5p-dependent transcriptional
activation but was ineffective toward a Gcn5p not regulated
gene. Consistently, acetylation of the histone H3 tail was
drastically reduced and provided a background level of
acetylated histone H3 similar to gcn5D. Following this
yeast-based method, we discovered that the quinolone
compound MC1626 is a selective inhibitor of Gcn5p in
vivo. Building on these results, we plan to investigate the
inhibitory activity of MC1626 in a wider spectrum of cases.
The compound may also be applied at the genomic level to
profile genomic expression upon addition of MC1626. For
profiling we will use the growth of gcn5 null strains and
their resistance to MC1626 treatment as a potential screen-
ing tool to define additional related target genes because
Gcn5p, being a global epigenetic regulator, may be
involved in the expression of acetylation-dependent gene
families. This approach may also be valuable for assessing
gene expression profiling in different external conditions
and upon addition of specific factors. Further tests will
clarify the mechanism of action of this very promising new
inhibitor, considering its high cell permeability, simple
structure, and high Gcn5p specificity tested in vivo. We
conclude by underlining the general deliverable of this
yeast-based method for wide, easy screening of HATs OFF
compounds.
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Acknowledgments
[21] Balasubramanyam K, Altaf M, Varier RA, Swaminathan V, Ravindran
A, Sadhale PP, et al. Polyisoprenylated benzophenone, garcinol, a
natural histone acetyltransferase inhibitor, represses chromatin tran-
This work was partially supported by RTL, CNR project
to PF, FIRB RBNE01KMT9, PRIN 2004 to A.M. and by
Fondazione Cenci-Bolognetti (Dr. P. Ballario).
scription and alters global gene expression.
J Biol Chem
2004;279:33716–26.
[22] Balasubramanyam K, Varier RA, Altaf M, Swaminathan V, Siddappa
NB, Ranga U, et al. Curcumin, a novel p300/CREB-binding protein-
specific inhibitor of acetyltransferase, represses the acetylation of
histone/non-histone proteins and histone acetyltransferase-dependent
chromatin transcription. J Biol Chem 2004;279:51163–71.
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