Evolution of the histone variant H2A.W reconstituted in fission yeast [ChIP-seq]
Diversification of histone variants is marked by the acquisition of distinct motifs and features through convergent evolution. H2A variants tend to be associated with defined domains of the genome. Specific features distinguish H2A variants in eukaryotes but whether evolution of these features predated the evolution of deposition mechanisms or vice-versa has remained unclear.In flowering plants, the variant H2A.W is tightly associated with heterochromatin. H2A.W evolved in land plants through acquisition of an extended C-terminal tail enriched with basic residues and a KSPK motif. Here, we used a synthetic approach in fission yeast, which lacks H2A.W and its dedicated deposition mechanism, to recapitulate the evolutionary steps that led to H2A.W and to assess the impact of the KSPK motif on heterochromatin composition and its properties. In conclusion, the acquisition of the KSPK motif in yeast promotes chromatin properties that are comparable to the properties and function of H2A.W in plant heterochromatin. Hence, the KSPK motif could have been selected before the evolution of direct heterochromatin deposition mechanisms. We propose that the acquisition of functional histone variant motifs can confer properties which affect only specific chromatin states, thereby driving the evolution of specific deposition mechanisms. Overall design: Genome-wide maps of H2A, H2A.Z and H3K9me2 in WT,spH2A.W and spH2A.W.4A  yeast strains