Regions of variant histone His2AvD required for Drosophila development

Abstract

One way in which a distinct chromosomal domain could be established to carry out a specialized function is by the localized incorporation of specific histone variants into nucleosomes. H2AZ, one such variant of the histone protein H2A, is required for the survival of Drosophila melanogaster, Tetrahymena thermophila and mice (R. Faast et al., in preparation). To search for the unique features of Drosophila H2AZ (His2AvD, also referred to as H2AvD) that are required for its essential function, we have performed amino-acid swap experiments in which residues unique to Drosophila His2AvD were replaced with equivalently positioned Drosophila H2A.1 residues. Mutated His2AvD genes encoding modified versions of this histone were transformed into Drosophila and tested for their ability to rescue null-mutant lethality. We show that the unique feature of His2AvD does not reside in its histone fold but in its carboxy-terminal domain. This C-terminal region maps to a short alpha-helix in H2A that is buried deep inside the nucleosome core.

Reconciling the positive and negative roles of histone H2A.Z in gene transcription

“…46 Moreover in yeast, the deletion of either the Gal4 or Pho4 activators did not influence the ability of H2A.Z to be enriched at model target genes of these respective activators (Lemieux K and Gaudreau L, unpublished data). 47 Conversely, in human cells, results obtained by our and other laboratories suggest that targeting of H2A.Z, by virtue of the p400 or SRCAP such as Tetrahymena thermophila, 15 Xenopus laevis, 16,17 Drosophila melanogaster 18,19 and mice, 20 suggesting that it may provide distinct functions among different organisms. In budding yeast, loss of H2A.Z leads to defects in transcriptional activation, alterations in transcriptional silencing, and increased chromosome loss.…”

Characterization of the Stability and Folding of H2A.Z Chromatin Particles

“…Indeed, in contrast to H2A.1/H2A.2 variants, histone H2A.Z has been shown to be essential for survival in organisms phylogenetically as diverse as Tetrahymena (11) and Drosophila (12, 13). It has been determined by substitution experiments with H2A.1 homologous regions that the indispensable portion of histone H2A.Z maps to the carboxyl-terminal of the molecule (13). Interestingly enough, of all core histones (H2A, H2B, H3, and H4), H2A is the only histone with a prominent carboxyl-terminal "tail" extending beyond the histone fold (39).…”

“…Despite this lack of effect on the DNA trajectory, it appears that internal protein-protein interactions are affected. Substitution of H2A Gln 104 by Gly 104 in H2A.Z destabilizes the 2(H2A.Z-H2B)-(H3-H4) 2 association and presents an opportune particle for DNA activation (13,17). Also the molecular surface of the variant nucleosome displays a novel acidic patch and a divalent cation-binding site, which may facilitate the rearrangement of higher order structure through internucleosomal electrostatic interactions or the recruitment of remodeling factors (21).…”

Chromatin Remodeling by Imitation Switch (ISWI) Class ATP-dependent Remodelers Is Stimulated by Histone Variant H2A.Z

“…Dependence of SNF2H stimulation on such residues would suggest that this activity plays an important role in vivo. In Drosophila, the essential region of H2A.Z homolog H2Av mapped to a 16-amino acid region encompassing an extended acidic patch along the surface of the nucleosome (27). Within this patch on H2A.Z, replacement of acidic residues Asp 94 and Ser 95 to the analogous residues found in H2A (Asn 94 and Lys 95 ) reduces the acidic patch to canonical size and mimics developmental defects upon H2A.Z depletion in Xenopus embryos (28).…”