Binding of Barrier to Autointegration Factor (BAF) to Histone H3 and Selected Linker Histones Including H1.1

Rocío Montes De Oca,Kenneth K Lee,Katherine L Wilson

doi:10.1074/jbc.m509917200

Rocío Montes De Oca, Kenneth K Lee + Show 1 more

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https://doi.org/10.1074/jbc.m509917200

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Abstract

Barrier to autointegration factor (BAF) is an essential conserved double-stranded DNA-binding protein in metazoans. BAF binds directly to LEM domain nuclear proteins (e.g. LAP2, Emerin, and MAN1), lamin A, homeodomain transcription factors, and human immunodeficiency virus type 1-encoded proteins. BAF influences higher order chromatin structure and is required to assemble nuclei. BAF also facilitates retroviral preintegration complex insertion into target DNA in vitro, through unknown mechanisms. We report that BAF binds directly and selectively to linker histone H1.1 (among three subtypes tested) and core histone H3 with affinities of approximately 700 nm and approximately 100-200 nm, respectively, in vitro and in vivo. Mutations at the bottom and top surfaces of the BAF dimer disrupted or enhanced, respectively, this binding and affected H1 and H3 similarly. Biochemical studies showed that C-terminal residues 108-215 of histone H1.1 and the N-terminal tail plus helix alphaN in the core of histone H3.1 were each necessary and sufficient to bind BAF. Based on its interactions with histones and DNA, we propose BAF might bind nucleosomes in vivo.

Highlights

Embryos, Barrier to autointegration factor (BAF) is present in both the cytoplasm and nucleus with significant enrichment near the nuclear envelope [12,13,14]
Most LEM domain proteins (e.g. LAP2␤, Emerin, MAN1) are lamin-binding proteins anchored at the nuclear inner membrane [22, 23]
We concluded that BAF binds core histone H3 and at least three of the seven linker histones that comigrate in SDS-polyacrylamide gels

Summary

Introduction

Embryos, BAF is present in both the cytoplasm and nucleus with significant enrichment near the nuclear envelope [12,13,14]. Most LEM domain proteins (e.g. LAP2␤, Emerin, MAN1) are lamin-binding proteins anchored at the nuclear inner membrane [22, 23]. Higher levels of added BAF (20 – 40% above endogenous) produce the opposite effect, blocking nuclear assembly and profoundly compacting chromatin [12]. These results showed that BAF influences chromatin structure and gene expression but did not reveal its mechanism. Linker histones range in mass from ϳ21–23 kDa and have a conserved tripartite domain organization [40] Their short N-terminal tail (“N-tail”) is proposed to bind DNA [41] and is post-translationally modified [42,43,44].

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