GenBank Accession numbers for the histone variants H2A.Z-1 and H2A.Z-2 used in the present work. The ANNOTATION field denotes: gene sequences newly isolated from draft genomes (in silico), gene sequences predicted as either H2A.Z-1 or H2A.Z-2 from databases and draft/complete genomes data (Pred), sequences defined either as H2A.Z-1 or H2A.Z-2 by the present analyses (a), sequences defined as H2A by the present analyses (b) and sequences whose annotation either as H2A.Z-1 or H2A.Z-2 has been corrected by the present work (c).