Toxoplasma gondii eukaryotic translation initiation factor 4A associated with tachyzoite virulence is down-regulated in the bradyzoite stage.

Comparative proteome analysis of mouse-virulent and attenuated Toxoplasma gondii strain revealed that steady-state synthesis of an unknown 53 kDa protein is markedly reduced in attenuated parasites. The results from protein microsequencing allowed isolation of a single-copy gene encoding a T. gondii homologue of eukaryotic translation initiation factor (eIF)4A. The deduced primary structure exhibits all sequence motifs typical of eIF4A. Differential expression of eIF4A between virulent and attenuated parasites was reconfirmed by immunoblot. Consistent with an involvement in the ribosomal preinitiation complex, the protein was localised in the tachyzoite extranuclear cytosol, being loosely associated with microsomal particles. Immunofluorescence detection of eIF4A in T. gondii stages of the intermediate host indicated that the protein is tachyzoite-specific. Stage-dependent expression is regulated at the transcriptional level as determined by reverse transcription-polymerase chain reaction and immunoblot. The down-regulation of eIF4A in attenuated T. gondii parasites and in the bradyzoite stage implies a role in tuning of the homeostasis of protein biosynthesis.