DNA fragments from human malaria parasites were cloned into Xgtll to produce a genomic DNA expression library. A pool of monoclonal antibodies (mAbs) recognizing three domains of the 195-kDa major merozoite surface glycoprotein (gp195) reacted with seven clones expressing malaria antigens. mAbs recognizing the 83-kDa product of gp195 reacted with the clones, but mAbs recognizing a glycosylated 45-kDa and a nonglycosylated 45-kDa domain did not.Restriction enzyme mapping revealed that the clones contained overlapping segments encoding about 70% of the gene beginning at the 5' end and ending at an EcoRI restriction enzyme site 3.3 kilobase pairs downstream. The mAbs recognizing the 83-kDa domain reacted differently with the clones, allowing the mapping of three epitopes, one of which was repetitive. Affinity-purified antibodies were selected from immune monkey serum with recombinant expression proteins adsorbed to nitrocellulose filters. When used to probe electrophoretic immunoblots of parasite extracts, these antigen-selected antibodies reacted with specific sets of processed products of gp195, including those associated with the 83-and the nonglycosylated 45-kDa domains. This information, combined with the mAb epitope map, allowed a tentative scheme for processing gp195 from the Camp strain to be proposed.Merozoites from Plasmodium falciparum malaria parasites have, as major components of their surface, a 195-kDa glycoprotein (gp195) (1) and polypeptides derived from this protein as a result of processing by proteases (2, 3). Processing of gp195 produces at least three smaller products found on the surface of merozoites (3) and has been observed in at least six P. falciparum strains (1,2,4,5). Processing occurs about the time merozoites are released from infected erythrocytes, and a series of transitory intermediates with molecular masses of about 153, 150, and 110 kDa appear (2). One of the final products has an Mr of 83 kDa (2, 4, 5) and possesses serotype-restricted epitopes (4, 5). Other products of 50 (1), 42, and 19 kDa (3) have been identified; the 50-kDa antigen is glycosylated (1) and may be homologous with the 42-kDa antigen. gp195 and its proteolytic products are recognized on intact merozoites by growth-inhibitory immune sera (6) and may be good candidates for vaccine development (1, 7-10).The molecular cloning and expression of parasite antigens in bacterial systems allows the preparation of sufficient amounts of pure antigen to conduct immunological and immunochemical studies. The cloning from cDNA of the complete structural gene encoding gp195 has been reported (11), and cDNA clones encoding 0.21 (7) and 1.1 (12) kilobase pairs (kb) of the gp195 gene have been reported as well. We report the cloning of a 3.6-kb portion of gp195 genomic DNA from the Camp strain and propose a scheme for processing the Camp strain protein, locating major proteolytic products and the positions of epitopes recognized by monoclonal antibodies (mAbs).MATERIALS AND METHODS Culture of P. falciparum. Camp strain...