The virulent Saimiri-adapted Palo Alto strain of Plasmodium falciparum does not express the ring-infected erythrocyte surface antigen.

The Palo Alto strain of Plasmodium falciparum is highly virulent for the Saimiri sciureus monkey. We have observed that these parasites do not express the Ring-infected erythrocyte surface antigene (RESA) gene. Immunoblots indicated that the Pf155/RESA protein was absent. The RESA mRNA could not be detected. Polymerase chain reaction and Southern blot analysis demonstrated that this lack of expression is due to gene rearrangements. The majority of the Palo Alto parasites have a deletion of the entire RESA gene, whereas in a minor fraction the RESA sequences remain detectable, but the 5' miniexon 1 is inverted. These data show that the RESA protein is dispensable for in vivo parasite growth, at least in Saimiri monkeys.