The intrinsic stability of H2B-ubiquitylated nucleosomes and their in vitro assembly/disassembly by histone chaperone NAP1.

Apart the gene-regulatory functions as docking sites for histone 'readers', some histone modifications could directly affect nucleosome structure. The H2BK34-ubiquitylation deposited by MOF-MSL complex, increases nucleosome dynamics in vitro and promotes donation of one H2A/H2B dimer to histone acceptors.We evaluated temperature-depended stability of H2BK34-ubiquitylated nucleosomes under 'physiological' ionic conditions in the presence or absence of histone acceptor, and examined assembly and disassembly of ubiquitylated nucleosomes in vitro by recombinant mouse NAP1.H2BK34ub modification is sufficient to promote selective eviction of only one H2A/H2B dimer independently of histone-binding agents. Despite the robust H2A/H2B dimer-displacement effect of mNAP1 with the H2BK34ub (but not unmodified) nucleosomes, NAP1 could assemble symmetrically- or asymmetrically ubiquitylated nucleosomes under 'physiological' conditions in vitro.The increased mobility of one nucleosomal H2A/H2B dimer is an intrinsic nucleosome destabilizing property of H2BK34 ubiquitylation that has the intranucleosome bases. The ability of NAP to reasonably efficiently assemble H2BK34-ubiquitylated nucleosomes supposes a potential mechanism for deposition/distribution of H2BK34ub mark in the MOF-MSL independent manner (for example, during histone dimer exchange upon transcription elongation).