ApiLoc - A database of published protein sub-cellular localisation in Apicomplexa

version 3 (curated until May 28, 2011)

Toxoplasma H2A variants reveal novel insights into nucleosome composition and functions for this histone family.

Dalmasso, M. C., Onyango, D. O., Naguleswaran, A., Sullivan, W. J. Jr, Angel, S. O. (2009 Sep 11, J Mol Biol)

Toxoplasma gondii is an obligate intracellular parasite. Toxoplasmosis is incurable because of its ability to differentiate from the rapidly replicating tachyzoite stage into a latent cyst form (bradyzoite stage). Gene regulation pertinent to Toxoplasma differentiation involves histone modification, but very little is known about the histone proteins in this early branching eukaryote. Here, we report the characterization of three H2A histones, variants H2AX and H2AZ, and a canonical H2A1. H2AZ is the minor parasite H2A member. H2A1 and H2AX both have an SQ motif, but only H2AX has a complete SQ(E/D)varphi (where varphi denotes a hydrophobic residue) known to be phosphorylated in response to DNA damage. We show that a novel H2B variant interacts with H2AZ and H2A1 but not with H2AX. Chromatin immunoprecipitation (ChIP) revealed that H2AZ and H2Bv are enriched at active genes while H2AX is enriched at repressed genes as well as the silent TgIRE repeat element. During DNA damage, we detected an increase in H2AX phosphorylation as well as increases in h2a1 and h2ax transcription. We found that expression of h2ax, but not h2a1 or h2az, increases in bradyzoites generated in vitro. Similar analysis performed on mature bradyzoites generated in vivo, which are arrested in G0, showed that h2az and h2ax are expressed but h2a1 is not, consistent with the idea that h2a1 is the canonical histone orthologue in the parasite. The increase of H2AX, which localizes to silenced areas during bradyzoite differentiation, is consistent with the quiescent nature of this stage of the life cycle. Our results indicate that the early-branching eukaryotic parasite Toxoplasma contains nucleosomes of novel composition, which is likely to impact multiple facets of parasite biology, including the clinically important process of bradyzoite differentiation.

PubMed: 19607843, full text

Localisation information

TGME49_105160 (H2Ba) histone H2B, putative

Experimental localisation: nucleus
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "As expected, each aH2A antibody stains the parasite nucleus (Fig. 3b)."
  • Microscopy type: Light
  • Microscopy method: polyclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: Taken directly from 16621068
  • Localisation record: Nucleus

TGME49_100200 (H2AZ) histone H2A

Experimental localisation: nucleus
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "As expected, each aH2A antibody stains the parasite nucleus (Fig. 3b)."
  • Microscopy type: Light
  • Microscopy method: polyclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: taken directly from publication
  • Localisation record: Nucleus

TGME49_061580 (H2AX) histone H2A, putative

Experimental localisation: nucleus
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "As expected, each aH2A antibody stains the parasite nucleus (Fig. 3b)."
  • Microscopy type: Light
  • Microscopy method: polyclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: taken directly from publication
  • Localisation record: Nucleus

TGME49_061250 (H2A1) histone H2A, putative

Experimental localisation: nucleus
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "As expected, each aH2A antibody stains the parasite nucleus (Fig. 3b)."
  • Microscopy type: Light
  • Microscopy method: polyclonal antibody directly to protein
  • Strain: RH
  • Gene model mapping comments: taken directly from publication
  • Localisation record: Nucleus

TGME49_009910 (H2Bv1, h2b) histone H2B variant 1

Experimental localisation: nucleus
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "The three histone variants co-IP with the acetylated-H3 histone (Fig. 5a). "
  • Microscopy type: ChIP
  • Microscopy method:
  • Strain: RH
  • Gene model mapping comments: annotation matches, 16621068 agrees with chromosome Ib
  • Localisation record: Nucleus