Abstracts (poster) - Wissenschaft Online

Stefan Ehrentraut, Jan Weber, Ann E. Ehrenhofer-Murray
The HDAC Rpd3 functions in boundary formation by removal of
Sir2 substrate
In Saccharomyces cerevisiae, spreading of the telomeric SIR heterochromatin is
prevented by the activity of boundary elements. So far, boundaries have been
associated with chromatin opening activities, like histone acetyltransferases (HATs) or
histone methyltransferases. Here, we show that the opposite enzymatic activity, the
histone deacetylase (HDAC) Rpd3, was necessary to prevent the encroachment of
heterochromatin into euchromatin at telomeres in S. cerevisiae.
We found by ChIP analysis that in the absence of Rpd3, the SIR complexes were
mislocalized to more centromere-proximal regions. Quantitative RT-PCR showed that SIR
proteins repressed subtelomeric genes in rpd3Δ cells, suggesting a role for Rpd3 in the
restriction of telomeric heterochromatin. When combined with the absence of a known
boundary factor, the HAT SAS-I, rpd3Δ caused inappropriate SIR spreading that was
lethal to yeast cells. Significantly, the lethality of sas2Δ rpd3Δ was suppressed by sir
deletions, suggesting parallel functions for the two enzymes in restricting SIR proteins to
heterochromatin. Furthermore, Rpd3 was capable of creating a boundary when targeted
to the telomere, demonstrating boundary function for Rpd3. Our experiments suggest
that histone deacetylation through Rpd3 deprives the HDAC Sir2 of the ability to
generate the metabolite O-acetyl-ADP-ribose during its NAD+-dependent deacetylation,
which then prevents SIR propagation along the chromatin fiber.
contact:
Stefan Ehrentraut
Universität Duisburg-Essen
Abteilung für Genetik
stefan.ehrentraut@uni-due.de
Universitätsstr. 5
45117 Essen (germany)