Gene inactivation of Pf11‐1 of Plasmodium falciparum by chromosome breakage and healing: identification of a gametocyte‐specific protein with a potential role in gametogenesis.

We report the identification of the product of the Plasmodium falciparum Pf11‐1 gene and demonstrate that it is a gametocyte‐specific protein that has a potential role in the rupture of the host erythrocyte and emergence of the gametes (gametogenesis). The Pf11‐1 gene is a large locus (30 kb) whose sequence predicts a glutamic acid‐rich polypeptide. Our identification of the Pf11‐1 gene product as gametocyte specific was greatly facilitated by the isolation of a mutant parasite clone in which greater than 90% of the Pf11‐1 gene was deleted. Molecular analysis of the mutant locus suggests that the underlying genetic mechanism is chromosome breakage and subsequent healing by the addition of telomere repeats. PCR‐based analysis showed that similar DNA rearrangements occur commonly in small subpopulations of most laboratory strains, suggesting that the Pf11‐1 locus represents a fragile chromosome region. Northern blot analysis demonstrates that a large Pf11‐1 gene‐specific transcript (much greater than 10 kb) is present in gametocytes but not in asexual blood stage parasites. The Pf11‐1 protein was localized by electron microscopy to granules in the cytoplasm of gametocytes adjacent to the membrane of the parasitophorous vacuole. Following in vitro stimulation of gametogenesis, the Pf11‐1 protein was found in the membrane of lysed erythrocytes, suggesting a role for Pf11‐1 in erythrocyte rupture within the mosquito gut.