Antifolate drug selection results in duplication and rearrangement of chromosome 7 in Plasmodium chabaudi.
We selected lines of Plasmodium chabaudi that are resistant to high levels of the antifolate drug pyrimethamine and have shown that rearrangement and duplication of a portion of chromosome 7 has occurred in the resistant lines. This chromosomal duplication results in an increase in the chromosome number from 14 to 15: two derived chromosomes (450 kilobases and 1.1 megabases) were smaller than the original chromosome 7 (1.3 megabases), so that essentially only a 200-kilobase region was duplicated. This region contained the DHFR-TS gene and the closely linked Hsp70 gene. We have macrorestriction mapped chromosome 7 from the pyrimethamine-susceptible line (DS) and also the duplicated chromosome 7s in the resistant line. From these maps, we have proposed a process for the karyotype changes. Sequencing of the DHFR gene from the parent and derived chromosomes showed that there were no mutations in the coding sequence. As a result of the duplication of the DHFR-TS gene, there is at least a twofold increase in expression of the DHFR-TS gene, and this may explain the ability of the pyrimethamine-resistant lines to grow in increased amounts of the drug.
Cowman
A F
AF
Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia.
Lew
A M
AM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002875:Chromosomes / Q000187:drug effects*; D004351:Drug Resistance; D015321:Gene Rearrangement; D005796:Genes; D008040:Genetic Linkage; D006360:Heat-Shock Proteins / Q000235:genetics; D007621:Karyotyping; D008969:Molecular Sequence Data; D005810:Multigene Family; D010961:Plasmodium / Q000187:drug effects / Q000235:genetics*; D011739:Pyrimethamine / Q000494:pharmacology*; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid
D006360:Heat-Shock Proteins; D011739:Pyrimethamine