Molecular characterization of surface antigen 3 (SAG3) gene of Toxoplasma gondii RH-IVRI strain.

Toxoplasmosis, caused by Toxoplasma gondii, is a zoonotic disease and is responsible for abortions, stillbirth, and neonatal complications in livestock, especially in sheep, goats, and pigs. The molecular characterization of the parasite having global distribution is considered important to delineate the phylogenetic relationship among different isolates/strains of the parasite. The present communication deals with the molecular cloning and sequence analysis of the 1,158 bp entire open reading frame of surface antigen 3 (SAG3) of T. gondii RH strain being maintained at the Indian Veterinary Research Institute (IVRI). The sequence comparison analysis revealed 99.9 % homology with the published sequence of T. gondii RH strain, with a single substitution of guanine 'G' instead of adenine 'A' at the 397th position of SAG3 sequence. The substitution of single nucleotide consequently resulted in the change of one amino acid residue of aspartic acid (D) instead of asparagine (N) present in the published sequence of RH strain. This denotes that the SAG3 gene of this RH strain has not undergone a major change in its molecular conformation even after repeated passage in mice for more than a decade at IVRI. The finding is important from the molecular phylogeny point of view.