SEQUENCE VARIATIONS IN THE PLASMODIUM-VIVAX DIHYDROFOLATE REDUCTASE-THYMIDYLATE SYNTHASE GENE AND THEIR RELATIONSHIP WITH PYRIMETHAMINE RESISTANCE

The gene encoding dihydrofolate reductase-thymidylate synthase of the human malaria parasite, Plasmodium vivax, was isolated by polymerase c hain reaction from genomic DNA and cloned. The sequences of the dihydr ofolate reductase domain of 30 clinical isolates originating from vari ous geographic areas were compared. Interstrain analysis revealed seve ral genotypic variations, including short tandem repeat arrays which p roduced length polymorphism between different parasite isolates and po int mutations in the putative dihydrofolate reductase active site cavi ty corresponding to those associated with pyrimethamine resistance in P. falciparum and rodent malaria parasites. Amino acid substitutions S er-->Asn-117 and Ser-->Arg-58 were associated with decreased level of in vitro pyrimethamine sensitivity. These findings suggest that the P. vivax dihydrofolate reductase domain is characterized by polymorphism that has not been observed in P. falciparum and may explain the resis tance of some P. vivax isolates to pyrimethamine. Nucleotide sequence data reported in this paper are available in the EMBL, GenBenk(TM) and DDJB databases under the accession numbers X98123 (isolate ARI!Pakist an), AJ003050 (isolate CNC/Thailand), AJ003051 (isolate COU/unknown ge ographic origin), AJ003052 (isolate DUF/French Guiana), AJ003053 (isol ate GRO/Madagascar), AJ003054 (isolate HRT/Comoros islands), AJ003071 (isolate LFT/Cambodia): AJ003072 (isolate LGF/India), AJ003073 (isolat e MAN/Comoros Islands), AJ003074 (isolate MAT/Surinam): AJ003075 (isol ate PHI/Djibouti), AJ003076 (isolate PIT/Madagascar), AJ003077 (isolat e YTZ/Indonesia), AJ222630 (isolate Burma-1), AJ222631 (isolate Burma- 151), AJ222632 (isolate Burma-5), AJ222633 (isolate Burma-6), AJ222634 (isolate Burma-98). (C) 1998 Elsevier Science B.V. All rights reserve d.