SEQUENCE CONSERVATION IN THE C-TERMINAL PART OF THE PRECURSOR TO THE MAJOR MEROZOITE SURFACE-PROTEINS (MSP1) OF PLASMODIUM-FALCIPARUM FROM FIELD ISOLATES

The C-terminal part of the precursor to the major merozoite surface proteins (MSP1) of Plasmodium falciparum contains potential protective epitopes and two cleavage sites for processing which take place prior to erythrocyte invasion by the merozoite. Since sequences available to date are limited and derived from cultured parasites, we have examined the extent of variations of this important part of the MSP1 gene from natural populations. Our sequence analyses of 1.6-1.7 kb from blocks 13-17 of the gene obtained from 19 Thai wild isolates have identified a deletion of a codon and 18 nucleotide substitutions, all of which are dimorphic substitutions and all but one create amino acid exchanges. However, residues at two cleavage sites for the C-terminus 42 kDa polypeptide and the 19-kDa polypeptide, a subfragment of the former, are conserved. Furthermore, all 12 cysteine residues at the C-terminal 19-kDa polypeptide are perfectly conserved, allowing the formation of 2 epidermal growth factor-like structures. These results indicate that in contrast to extensive variations at the N-terminal part of MSP1, limited variations occur at the C-terminal part.