Interallelic recombination in the merozoite surface protein 1 (MSP-1) gene of Plasmodium vivax from Thai isolates.

The merozoite of Plasmodium vivax possesses a high molecular mass surface protein called Pv-merozoite surface protein 1, PvMSP-1, which exhibits antigenic diversity among isolates. In this study, the extent of sequence variation in the polymorphic region and the flanking interspecies conserved blocks (ICBs) 5 and 6 of the PvMSP-1 gene was analyzed using the polymerase chain reaction to amplify the DNA fragment encompassing these regions, followed by sequencing. Twenty different alleles were obtained from 15 Thai isolates. Results revealed five distinct sequence types of the polymorphic region, two of which were newly identified in this study: one probably generated by intragenic recombination at a site different from that previously reported and the other by duplication of a 30 nucleotide (nt) sequence at the 3' end of the region. On the other hand, almost all nucleotide substitutions in the flanking regions, ICB5 and ICB6, were dimorphic, creating microheterogeneity in the region. Furthermore, stretches of nucleotide substitutions were found to be linked in ICB6, suggesting the potential recombination sites between these stretches. It is also noted that extensive sequence variation in the PvMSP-1 gene and coinfection with different PvMSP-1 alleles occurred among the P. vivax population in the endemic areas of Thailand.