THE EVOLUTIONARY ORIGIN OF THE 35 KB CIRCULAR DNA OF PLASMODIUM-FALCIPARUM - NEW EVIDENCE SUPPORTS A POSSIBLE RHODOPHYTE ANCESTRY

In common with other Apicomplexan parasites, Plasmodium falciparum car ries two extrachromosomal DNAs, one of which, the 6 kb element, is und oubtedly mitochondrial. The second, generally referred to as the 35 kb circle, is of unknown provenance, but the nature and organization of its genetic content makes a mitochondrial association unlikely and the molecule has features reminiscent of plastid genomes. We now report t he occurrence on the circle of an open reading frame specifying a pred icted 470 amino acid protein that shares more than 50% identity with a gene currently known only on the plastome of red algae. This high deg ree of conservation confirms the 35 kb circle's plastid ancestry, and we speculate that it may have originated from the rhodoplast of an anc ient red algal endosymbiont in the progenitor of the Apicomplexa.