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 t he Saimiri sciureus monkey. We have observed that these parasites do n ot express the Ring-infected erythrocyte surface antigene (RESA) gene. Immunoblots indicated that the Pf155/RESA protein was absent. The RES A mRNA could not be detected. Polymerase chain reaction and Southern b lot analysis demonstrated that this lack of expression is due to gene rearrangements. The majority of the Palo Alto parasites have a deletio n of the entire RESA gene, whereas in a minor fraction the RESA sequen ces remain detectable, but the 5' miniexon 1 is inverted. These data s how that the RESA protein is dispensable for in vivo parasite growth, at least in Saimiri monkeys.