POLE3-POLE4 Is a Histone H3-H4 Chaperone that Maintains Chromatin Integrity during DNA Replication

Summary

Maintenance of epigenetic integrity relies on coordinated recycling and partitioning of parental histones and deposition of newly synthesized histones during DNA replication. This process depends upon a poorly characterized network of histone chaperones, remodelers, and binding proteins. Here we implicate the POLE3-POLE4 subcomplex of the leading-strand polymerase, Polε, in replication-coupled nucleosome assembly through its ability to selectively bind to histones H3-H4. Using hydrogen/deuterium exchange mass spectrometry and physical mapping, we define minimal domains necessary for interaction between POLE3-POLE4 and histones H3-H4. Biochemical analyses establish that POLE3-POLE4 is a histone chaperone that promotes tetrasome formation and DNA supercoiling in vitro. In cells, POLE3-POLE4 binds both newly synthesized and parental histones, and its depletion hinders helicase unwinding and chromatin PCNA unloading and compromises coordinated parental histone retention and new histone deposition. Collectively, our study reveals that POLE3-POLE4 possesses intrinsic H3-H4 chaperone activity, which facilitates faithful nucleosome dynamics at the replication fork.

Graphical Abstract

Highlights

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  Mammalian POLE3-POLE4 is a bona fide H2A-H2B histone fold complex

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  The POLE3-POLE4 complex binds to histones H3-H4 in vitro and in vivo

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  POLE3-POLE4 induces tetrasome formation and DNA supercoiling in vitro

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  POLE3-POLE4 chaperone activity promotes chromatin integrity in mammalian cells

Abstract

Bellelli et al. report that mammalian POLE3-POLE4 binds to histones H3-H4 and promotes tetrasome formation and DNA supercoiling, acting as a bona fide histone chaperone. Consistent with this, cells lacking POLE3/POLE4 exhibit defective RPA accumulation and PCNA retention on chromatin, features of defective chromatin dismantling/maturation at the replication fork.