Plasmodium falciparum: characterization of gene R45 encoding a trophozoite antigen containing a central block of six amino acid repeats.

We describe here an antigen, called R45, expressed by the young trophozoites of Plasmodium falciparum. This antigen contains a block of tandem repeats of six amino acids which are recognized by sera from humans living in endemic areas. The R45 gene is located on chromosome 3. It is present in all strains examined and shows limited size polymorphism. The C-terminal unique region of the protein shows a strong homology with the catalytic domain of the serine protein kinases. Interestingly, the central repeats contain a large number of putative phosphorylation sites. The implications of these features are discussed.