Preferential induction of H2A.Y in ΔTXR1 cells. Induction of the histone variant H2A.Y in ΔTXR1 cells, as demonstrated by MS and microarray analyses. A, Selected tandem MS of H2A.Y peptide precursor ion of 1031.0866 Da (Z = 2+, mass error = 1ppm, Ion score = 113). The peptide corresponds to H2A.Y residues 143–160: NLVFNLFPSLVILDTLDK. All fragment ions were accounted for. H2A.Y peptides were detected by MS only in ΔTXR1 cells. B, induction of H2A.Y mRNA levels in ΔTXR1 cells. HTAY gene (encoding H2A.Y protein) was significantly induced in ΔTXR1 cells (>9 folds, p < 0.01) whereas genes encoding all other histones remained mostly unchanged.