Third form of the precursor to the major merozoite surface antigens of Plasmodium falciparum.

The precursor to the major merozoite surface antigens of Plasmodium falciparum appears to be encoded by two distinctly different (dimorphic) alleles able to undergo limited recombination. We analyzed 18 previously uncharacterized P. falciparum isolates to test the dimorphic model. All but one, a Thailand isolate, conformed to the dimorphic model, and this isolate conformed to the dimorphic model in all but variable block 2. Sequence analysis revealed that block 2 of isolate CSL2 was a third form. Hence, the dimorphic model is not strictly correct. Recombination between alleles was found only within two conserved blocks near the 5' end of the gene.