Repetitive sequences upstream of the pfg27/25 gene determine polymorphism in laboratory and natural lines of Plasmodium falciparum

The structure of the genomic region located upstream of the gametocyte-spec ific gene pfg 27/25 of Plasmodium falciparum was analysed in laboratory lin es and field isolates of the parasite. The gene is located in a subtelomeri c region of chromosome 13 in parasite clones 3D7 and HB3. Analysis of labor atory lines and field isolates of P. falciparum indicated that polymorphism upstream of pfg27/25 is mainly due to the structure of a repetitive DNA re gion located at about half a kilobase from the pfg27/25 coding sequence. Di fferent types of repetitive sequences are present in this region, whose cop y number is Variable in different parasite lines. In addition a GC-rich seq uence element contained in this region, which is proposed to be the startpo int of pfg27/25 mRNA, presents either a direct or a reverse orientation in different parasite lines. Genomic deletions upstream of the pfg27/25 gene a re also described in two laboratory lines of the parasite, which eliminate two newly identified malaria genes, orf P and orf Gap, from the genome of t hese parasites. One of them, orf cap, deleted from the reference parasite c lone 3D7, is abundantly expressed as mature mRNA in asexual parasites. PCR analysis on 64 field isolates of P. falciparum indicated that orf P and orf Gap sequences are present in all tested samples of naturally propagating p arasites. (C) 2000 Elsevier Science B.V. All rights reserved.