DISRUPTION OF A NOVEL OPEN READING FRAME OF PLASMODIUM-FALCIPARUM CHROMOSOME-9 BY SUBTELOMERIC AND INTERNAL DELETIONS CAN LEAD TO LOSS OR MAINTENANCE OF CYTOADHERENCE

Isolates of Plasmodium falciparum commonly undergo a large subtelomeri c deletion of the right end of chromosome 9 during in vitro cultivatio n, accompanied by loss of ability to cytoadhere to melanoma cells and greatly lowered gametocyte production. ItG2, an isolate in which cytoa dherence is stable, has undergone a subtelomeric deletion of intermedi ate length on chromosome 9. We show here that the deletions in all non -cytoadherent clones examined have breakpoints within or delete a nove l open reading frame (the breakpoint open reading frame, BPORF) that i s a unique sequence in the genome. Surprisingly, in ItG2 BPORF has bee n removed by an additional 15 kb internal deletion in chromosome 9. Th ese results suggest mechanisms to account for the observed frequent de letion of the right arm of chromosome 9 and for the known stability of cytoadherence in ItG2. However, we were unable to detect var genes in this region of the ItG2 genome. We conclude that the product of a nov el gene distinct from the var family is implicated in cytoadherence.