Molecular Cell
Volume 19, Issue 5, 2 September 2005, Pages 707-716
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Short Article
Barrier Function at HMR

https://doi.org/10.1016/j.molcel.2005.07.022Get rights and content
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Summary

The silenced HMR domain is restricted from spreading by barrier elements, and the right barrier is a unique t-RNATHR gene. We show that sequences immediately flanking the silenced domain were enriched in acetylated, but not methylated, histones, whereas the barrier element was associated with a nucleosome-free region. Surprisingly, the SAGA acetyltransferase resided across the entire region. We further demonstrate that a mutation in the barrier eliminated the nucleosome-free gap but only subtly altered the distribution of SAGA. Interestingly, neither reformation of the nucleosome nor mutations in chromatin-modifying enzymes alone led to an unrestricted spread of silenced chromatin. Double mutations in the t-RNA barrier and these complexes, on the other hand, led to a significant spread of Sir proteins. These results suggest two overlapping mechanisms function to restrict the spread of silencing: one of which involves a DNA binding element, whereas the other mechanism involves specific chromatin-modifying activities.

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