Sequence diversity in the intron of the calmodulin gene from Plasmodium falciparum

Sequence variation in the single intron of the calmodulin gene of Plasmodium falciparum has been examined following amplification using the polymerase chain reaction (PCR). The intron has 4 repeating motifs varying in length: 3 of these contain a dinunucleotide repeat, dA-dT, the fourth is a pentameric repeating unit, dA-dT-dA-dT-dT. These DNA polymorphisms can be applied to the study of parasite populations in mixed infections and in strain identification. The function of these repeating motifs is unknown. Computer modelling of the possible intron structures demonstrates that each of these repeating motifs forms individual stem loops such that any changes in repeat number are self-compensatory and do not change the overall intron structure. The implications of this sequence variation are discussed.