A histone variant, H2AvD, is essential in Drosophila melanogaster

H2AvD, a Drosophila melanogaster histone variant of the H2A.Z class, is encoded by a single copy gene in the 97CD region of the polytene chromosomes. Northern analysis shows that the transcript is expressed in adult females and is abundant throughout the first 12 h of embryogenesis but then decreases. The H2AvD protein is present at essentially constant levels in all developmental stages. Using D. melanogaster stocks with deletions in the 97CD region, we have localized the H2AvD gene to the 97D1-9 interval. A lethal mutation in this interval, l(3)810, exhibits a 311-base pair deletion in the H2AvD gene, which removes the second exon. P-element mediated transformation using a 4.1-kilobase fragment containing the H2AvD gene rescues the lethal phenotype. H2AvD is therefore both essential and continuously present, suggesting a requirement for its utilization, either to provide an alternative capability for nucleosome assembly or to generate an alternative nucleosome structure.