title: Amino acid changes linked to pyrimethamine resistance in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum.
abstract: We describe the isolation and the sequence of the gene for the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS; EC 1.5.1.3 and EC 2.1.1.45, respectively) from two pyrimethamine-resistant clones of Plasmodium falciparum, HB3 and 7G8. We have also derived the sequence of the DHFR portion of the gene, by amplification using polymerase chain reaction, for the pyrimethamine-sensitive clone 3D7 and the pyrimethamine-resistant strains V-1, K-1, Csl-2, and Palo-alto. The deduced protein sequence of the resistant DHFR portion of the enzyme from HB3 contained a single amino acid difference from the pyrimethamine-sensitive clone 3D7. It is highly likely that this difference is involved in the mechanism of drug resistance in HB3. The sequence of the DHFR gene from other pyrimethamine-resistant strains contains the same amino acid difference from the sensitive clone 3D7. However, they all differ at one other site that may influence pyrimethamine resistance. The DHFR-TS gene is present as a single copy on chromosome 4 in all pyrimethamine-sensitive and pyrimethamine-resistant isolates tested. Therefore, the molecular basis of pyrimethamine resistance in the parasites tested is not amplification of the DHFR-TS gene.
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Victoria, Australia.
authors.forename: A F
authors.initials: AF
authors.lastname: Cowman
authors.forename: M J
authors.initials: MJ
authors.lastname: Morry
authors.forename: B A
authors.initials: BA
authors.lastname: Biggs
authors.forename: G A
authors.initials: GA
authors.lastname: Cross
authors.forename: S J
authors.initials: SJ
authors.lastname: Foote
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004351:Drug Resistance / Q000235:genetics; D005796:Genes / Q000187:drug effects*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics*; D010963:Plasmodium falciparum / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D011739:Pyrimethamine / Q000494:pharmacology*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D013940:Thymidylate Synthase / Q000235:genetics*
chemical_list: D009097:Multienzyme Complexes; C056930:thymidylate synthase-dihydrofolate reductase; D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; D011739:Pyrimethamine