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SIR proteins create compact heterochromatin fibers

Authors :
Scot A. Wolfe
Sarah G. Swygert
Subhadip Senapati
Craig L. Peterson
Stuart Lindsay
Mehmet Fatih Bolukbasi
Source :
Proceedings of the National Academy of Sciences. 115:12447-12452
Publication Year :
2018
Publisher :
Proceedings of the National Academy of Sciences, 2018.

Abstract

SummaryHeterochromatin is a silenced chromatin region essential for maintaining genomic stability and driving developmental processes. The complicated structure and dynamics of heterochromatin have rendered it difficult to characterize. In budding yeast, heterochromatin assembly requires the SIR proteins -- Sir3, believed to be the primary structural component of SIR heterochromatin, and the Sir2/4 complex, responsible for the targeted recruitment of SIR proteins and the deacetylation of lysine 16 of histone H4. Previously, we found that Sir3 binds but does not compact nucleosomal arrays. Here we reconstitute chromatin fibers with the complete complement of SIR proteins and use sedimentation velocity, molecular modeling, and atomic force microscopy to characterize the stoichiometry and conformation of SIR chromatin fibers. In contrast to previous studies, our results demonstrate that SIR arrays are highly compact. Strikingly, the condensed structure of SIR heterochromatin fibers requires both the integrity of H4K16 and an interaction between Sir3 and Sir4. We propose a model in which two molecules of Sir3 bridge and stabilize two adjacent nucleosomes, while a single Sir2/4 heterodimer binds the intervening linker DNA, driving fiber compaction.

Details

ISSN :
10916490 and 00278424
Volume :
115
Database :
OpenAIRE
Journal :
Proceedings of the National Academy of Sciences
Accession number :
edsair.doi.dedup.....411e802e8e12238c3bf826bc3097d74d
Full Text :
https://doi.org/10.1073/pnas.1810647115