Mutation rates in the dihydrofolate reductase gene of Plasmodium falciparum

S.  PAGET-MCNICOL  a1 c1 and A.  SAUL  a2
a1 The University of Queensland and the Malaria and Arbovirus Unit, Queensland Institute of Medical Research, QLD 4029, Australia
a2 Malaria Vaccine Development Unit, NIAID/LPD, National Institutes of Health, Rockville, MD 20852, USA

Article author query
paget-mcnicol s   [PubMed][Google Scholar] 
saul a   [PubMed][Google Scholar] 


A new method has been established to define the limits on a spontaneous mutation rate for a gene in Plasmodium falciparum. The method combines mathematical modelling and large-scale in vitro culturing and calculates the difference in mutant frequencies at 2 separate time-points. We measured the mutation rate at 2 positions in the dihydrofolate reductase (DHFR) gene of 3D7, a pyrimethamine-sensitive line of P. falciparum. This line was re-cloned and an effectively large population was treated with a selective pyrimethamine concentration of 40 nM. We detected point mutations at codon-46 (TTA to TCA) and codon-108 (AGC to AAC), resulting in serine replacing leucine and asparagine replacing serine respectively in the corresponding gene product. The substitutions caused a decrease in pyrimethamine sensitivity. By mathematical modelling we determined that the mutation rate at a given position in DHFR was low and occurred at less than 2.5×10−9 mutations/DHFR gene/replication. This result has important implications for Plasmodium genetic diversity and anti-malarial drug therapy by demonstrating that even with low mutation rates anti-malarial resistance will inevitably arise when mutant alleles are selected under drug pressure.

(Received August 8 2000)
(Revised November 17 2000)
(Accepted November 28 2000)

Key Words: dihydrofolate reductase; mutation rate; malaria; mathematical modelling; Plasmodium falciparum.

c1 Corresponding author: Malaria and Arbovirus Unit, The Queensland Institute of Medical Research, QLD 4029, Australia. Tel: +61-7-33620420. Fax: +61-7-33620104. E-mail: