title: Pyrimethamine resistant mutations in Plasmodium falciparum.
abstract: Three mutations in Plasmodium falciparum yielding increased resistance to pyrimethamine were obtained following treatment with chemical mutagens and selection in presence of pyrimethamine. From parasite clone TM4/8.2 a mutant, TM4/8.2/4.1, was produced which raised pyrimethamine resistance about 500 times and was found to involve an amino acid change in the DHFR-TS enzyme molecule from Ser108 to Asn108. A clone of another isolate, T9/94, yielded a mutant, T9/94/300.300, raising pyrimethamine resistance about 10 times and involving an amino acid change from Ile164 to Met164. However, another mutant from T9/94, T9/94/M1-1(b3), although it raised the pyrimethamine resistance 100 times, did not involve any changes in the coding sequence of the DHFR-TS gene, but resulted in the production of about twice as much DHFR-TS enzyme as the original clone T9/94. No amplification of the DHFR-TS gene was detected. It is concluded that changes in pyrimethamine resistance of malaria parasites may arise in at least 2 ways: (1) by structural changes in the DHFR domain of the DHFR-TS gene (as previously found by other workers); (2) by other changes, possibly affecting the expression of the DHFR-TS gene. The relative importance of these 2 mechanisms in causing resistance in wild populations of P. falciparum is discussed.
authors.affiliation: Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
authors.forename: S
authors.initials: S
authors.lastname: Thaithong
authors.forename: S W
authors.initials: SW
authors.lastname: Chan
authors.forename: S
authors.initials: S
authors.lastname: Songsomboon
authors.forename: P
authors.initials: P
authors.lastname: Wilairat
authors.forename: N
authors.initials: N
authors.lastname: Seesod
authors.forename: T
authors.initials: T
authors.lastname: Sueblinwong
authors.forename: M
authors.initials: M
authors.lastname: Goman
authors.forename: R
authors.initials: R
authors.lastname: Ridley
authors.forename: G
authors.initials: G
authors.lastname: Beale
mesh_terms: D000818:Animals; D001483:Base Sequence; D004351:Drug Resistance / Q000235:genetics; D006801:Humans; D016778:Malaria, Falciparum / Q000469:parasitology; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics*; D016296:Mutagenesis; D009154:Mutation; D009838:Oligodeoxyribonucleotides / Q000235:genetics; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D016133:Polymerase Chain Reaction; D011739:Pyrimethamine / Q000494:pharmacology*; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry / Q000235:genetics*; D013940:Thymidylate Synthase / Q000737:chemistry / Q000235:genetics*
chemical_list: D009097:Multienzyme Complexes; D009838:Oligodeoxyribonucleotides; C056930:thymidylate synthase-dihydrofolate reductase; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; D011739:Pyrimethamine