CONSERVATION OF THE PLASMODIUM-FALCIPARUM SPOROZOITE SURFACE PROTEIN GENE, STARP, IN-FIELD ISOLATES AND DISTINCT SPECIES OF PLASMODIUM

The extent of structural conservation of the Plasmodium falciparum spo rozoite surface protein gene, STARP, recently characterized in the T9/ 96 clone, has been analyzed using the polymerase chain reaction. Resul ts from Ivory Coast and Thai clones, field isolates originating from B razil and Kenya and laboratory-maintained strains strongly suggest tha t this gene has a highly conserved structure throughout this species. This structure includes a complex repetitive central domain consisting of a mosaic region followed by tandem 45-amino acid-encoding (Rp45) a nd 10-amino acid-encoding (Rp10) repeat regions. Limited size variatio n in this domain appeared to result from highly localized duplication events in the Rp45 and Rp10 regions. No size variation was observed in the 5' and 3' coding non-repetitive regions, but minor size polymorph ism was found in the single intron at the 5' end of the gene. No evide nce was found of distinct families of polymorphic types, as has been o bserved with the blood-stage MSA-1, MSA-2 and S-antigens. The sequence of the STARP homologue in the phylogenetically close chimpanzee paras ite, Plasmodium reichenowi, has also been elucidated and reveals high sequence conservation, although interesting differences were detected in the composition of the Rp10 region, known in P. falciparum to conta in B- and T-cell epitopes. Finally, DNA hybridization reveals the pres ence in rodent malaria species of sequences containing homology to the STARP non-repetitive (though not the repetitive) regions, which would suggest that a similar, conserved gene may exist in these species.