Demonstration of alternative splicing of a pre-mRNA expressed in the blood stage form of Plasmodium falciparum.

By screening of a lambda gt11 library from Plasmodium falciparum genomic DNA with an antiserum raised against a 41-kDa protein band, which was shown to confer protective immunity to monkeys, the phage clone 41-3 was identified. The entire 41-3 gene was isolated, and its coding regions were determined by amplification and sequencing of 41-3 specific mRNA fragments. The 41-3 gene has a complex structure consisting of nine exons, encoding 375 amino acids in total with a calculated molecular weight of 43,400. Provided that the N-terminal hydrophobic residues function as signal sequence which is cleaved off, the molecular weight of the 41-3 protein decreases to 41,200 and could therefore be considered to be a component of the protective Mr = 41,000 protein band. Indeed, a 41-kDa protein could be detected by Western blot analysis using antisera raised against different recombinant expression products of the 41-3 gene. We furthermore demonstrate an alternative splice process for the mRNA precursor transcribed from the 41-3 gene to yield at least three distinct mRNAs. The major splice product carries all exons E1 to E9, whereas at least two minor 41-3 mRNA species can be identified which show deletions in the region between exons E5 and E7. The possible role of this differential splice process for the parasite is discussed.