2 ALLELES OF THE 175-KILODALTON PLASMODIUM-FALCIPARUM ERYTHROCYTE BINDING ANTIGEN

EBA-175, erythrocyte binding antigen 175, is a 175-kDa antigen of Plas modium falciparum which has been shown to be involved in the recogniti on of erythrocytes by merozoites and may be involved in the process of erythrocyte invasion. Invasion of erythrocytes by Camp strain merozoi tes is inhibited by pre-treatment of red blood cells by EBA-175 from t he heterologous strain, FCR-3. The sequence of the Camp strain has bee n published and we report here the sequence of the FCR-3 strain. The s equences are nearly identical except for a 423-bp segment in the FCR-3 strain, F-segment, that is not found in the Camp strain and a 342-bp segment, C-segment, present in the Camp strain but not in the FCR-3 st rain. The locations of these two segments are different in Camp and FC R-3 EBA-175 genes and there is little DNA or amino acid sequence homol ogy between them. The essentially dimorphic alleles, F-segment and C-s egment, are conserved in all isolates examined to date. Evidence of ge netic cross-over between the FCR-3 and the Camp EBA-175 genes was not observed in the analysis of a limited number of wild isolates. The con tinued study of the biological relevance of these sequence divergences in EBA-175 may further elucidate the sequence of events resulting in merozoite invasion of erythrocytes.