Activation of facultatively silenced Drosophila loci associates with increased acetylation of histone H2AvD.

H2A.Z is an evolutionarily highly conserved non-allelic variant of histone H2A. H2A.Z and its homologues have been shown to involve in both chromatin silencing and activation. Although much of our knowledge of H2A.Z biological activity has come from studies on its yeast homologue Htz1, H2A.Z appears to have more complex and diverse functions in higher eukaryotes. To investigate the involvement of H2AvD, a Drosophila homologue of mammalian H2A.Z, in mechanisms of conditional activation of facultatively silenced genes, we generated transgenic Drosophila lines expressing H2AvD fused at the C- or N-terminus with the green fluorescent protein (GFP). Using heat shock-induced gene activation and polytene chromosome puff formation as an in vivo model system, we analyzed effects of H2AvD termini modifications on transcription. We found that N-terminally fused GFP inhibited H2AvD acetylation and impaired heat shock-induced puff formation and hsp70 gene activation. Our data suggest that the N-terminal region of H2AvD plays a pivotal role in transcriptional activation and that induction of transiently silenced Drosophila loci associates with increased acetylation of H2AvD.