Cloning and characterization of a novel histone acetyltransferase homologue from the protozoan parasite Toxoplasma gondii reveals a distinct GCN5 family member.

In an effort to identify gene products involved in transcriptional regulation in apicomplexan parasites, the Toxoplasma gondii expressed sequence tag (EST) database was examined for sequences containing similarity to known transcriptional components. One EST (dbEST ID #466792) exhibited strong similarity to yeast GCN5 and other histone acetyltransferases (HATs). Primers were designed based on the EST sequence and used to amplify an 850 bp fragment (containing an intron) from T. gondii genomic DNA which was used to identify four cDNA clones from a tachyzoite cDNA library. The complete open reading frame (ORF) of 3.5 kb was elucidated using 5' RACE and genomic sequence. The deduced amino acid sequence of the coding region shows that the C-terminal domain possesses unequivocal similarity to GCN5 family members. However, unlike other lower eukaryotes, T. gondii GCN5 has an extended N-terminal domain similar in length, but not in composition, to metazoan HAT proteins. These features distinguish T. gondii GCN5 as a novel member of the GCN5 family. A portion of the cDNA sequence was used as a probe to isolate three overlapping clones from a T. gondii genomic library, generating a approximately 7.5 kb map of the GCN5 locus which contains seven exons separated by six introns. Southern analysis verifies the predicted map and suggests that a similar locus may be present elsewhere in the genome.