THE EXPRESSION OF TOXOPLASMA PROTEINS IN NEOSPORA-CANINUM AND THE IDENTIFICATION OF A GENE ENCODING A NOVEL RHOPTRY PROTEIN

Genes for the Toxoplasma gondii dense granule and rhoptry proteins nuc leoside triphosphate hydrolase 3 and ROP2 were expressed at high level s in the closely related parasite N. caninum. The protein products wer e processed appropriately and were targeted to their correct secretory organelles. NTPase 3 was secreted into the parasitophorous vacuole. T he utility of this system was demonstrated in the analysis of a new op en reading frame identified upstream of two identical copies of the RO P2 gene. The unknown open reading frame was introduced into Neospora, and transfected parasites were analyzed by immunoblot with antibodies to known T. gondii rhoptry protein families. The transfected Neospora expressed a novel 52 kDa protein, designated ROP8, which localized in the rhoptries. These results illustrate that transfection of known Tox oplasma genes into N. caninum can be used to study their expression, p rocessing and targeting in an immunologically distinct backgronnd. The y also illustrate the usefulness of N. caninum transfection in the ide ntification and subcellular distribution of proteins encoded by previo usly uncharacterized Toxoplasma genes. (C) 1997 Elsevier Science B.V.