Strain variation in the circumsporozoite protein gene of Plasmodium falciparum

The complete nucleotide sequence of the cloned circumsporozoite protein gene of the Plasmodium falciparum Wellcome (West African) isolate has been determined. The sequence shows two striking differences from that of the published Brazilian strain; the total number of tandem 12 base pair repeats is 46 compared to 41, and the 5′ coding region contains an additional 30 nucleotides. From Southern blot experiments, two out of four cloned Thai lines also have a similar, higher number of repeats. Heterogeneity in the CSP gene repeat region and in the length of the 5′ coding region allows the strains to be classed into three groups, with the Wellcome strain being indistinguishable from the Thai line T9-94.