Molecular cloning, genomic structure and localization in a blood stage antigen of Plasmodium falciparum characterized by a serine stretch

Two short DNA segments were isolated by screening of a lambda gt11 library from Plasmodium falciparum schizont cDNA with an antiserum against the 140 kDa protein, which confers protective immunity to monkeys. The segments were used to identify a genomic fragment which carries the entire coding sequence for a protein of 113 kDa characterized by a stretch of serine residues (SERP I). We present the complete nucleotide and deduced amino acid sequence as well as the structure of the SERP I gene. The gene consists of four exons interrupted by three short introns located at the amino-terminal half. Exon 1 and the first part of exon 2 code for hydrophobic amino acids of a putative signal sequence. Exon 2 contains two repetitive segments, the first encoding six glycine rich octapeptides and a second region coding for 37 consecutive serine residues. Southern blot analysis demonstrated the conservation of the SERP I gene in four different parasite strains. SERP I could be localized in the parasitophorous vacuole and in the surrounding membranes. We discuss the relationship of this protein to the recently described P126 polypeptide and the possible role of this antigen as a vaccine candidate.