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H3K9 methylation extends across natural boundaries of heterochromatin in the absence of an HP 1 protein
Author(s) -
Stunnenberg Rieka,
KulasegaranShylini Raghavendran,
Keller Claudia,
Kirschmann Moritz A,
Gelman Laurent,
Bühler Marc
Publication year - 2015
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.15252/embj.201591320
Subject(s) - heterochromatin , euchromatin , biology , heterochromatin protein 1 , constitutive heterochromatin , methylation , non histone protein , genetics , transcription (linguistics) , chromatin , gene , linguistics , philosophy
Proteins of the conserved HP 1 family are elementary components of heterochromatin and are generally assumed to play a central role in the creation of a rigid, densely packed heterochromatic network that is inaccessible to the transcription machinery. Here, we demonstrate that the fission yeast HP 1 protein Swi6 exists as a single highly dynamic population that rapidly exchanges in cis and in trans between different heterochromatic regions. Binding to methylated H3K9 or to heterochromatic RNA decelerates Swi6 mobility. We further show that Swi6 is largely dispensable to the maintenance of heterochromatin domains. In the absence of Swi6, H3K9 methylation levels are maintained by a mechanism that depends on polymeric self‐association properties of Tas3, a subunit of the RNA ‐induced transcriptional silencing complex. Our results disclose a surprising role for Swi6 dimerization in demarcating constitutive heterochromatin from neighboring euchromatin. Thus, rather than promoting maintenance and spreading of heterochromatin, Swi6 appears to limit these processes and appropriately confine heterochromatin.