Histone variant H2A.Z inhibits transcription in reconstituted nucleosomes

The existence of histone nonallelic variants has been known for more than 30 years, but only recently have we acquired significant insights into their functions. Nucleosomes containing histone variants are nonrandomly distributed in genomes and may impart different biological functions to the relevant chromatin regions. We have used the model T7 RNA polymerase to transcribe reconstituted nucleosomes containing either canonical human recombinant histones or two histone variants, H2A.Z or H3.3, whose presence has been associated with active transcription. Remarkably, in contrast to canonical and H3.3-containing nucleosomes, H2A.Z-containing nucleosomes were refractive to transcription, with residual levels of transcription determined by the sequence of the underlying DNA template. To our knowledge, this is the first example of a nucleosome that is intrinsically untranscribable.