Deletion mutagenesis of large areas in Plasmodium falciparum genes: a comparative study

The increasing emergence of Plasmodium falciparum parasites resistant to most of the cost-effective drugs has necessitated the identification of novel leads and drug targets. Parasite-specific inserts in enzymes that are essential for the differentiation and proliferation of malarial parasites have received considerable interest since it distinguishes these proteins from their human counterparts. The functions of these inserts, which include mediations of protein activities or protein-protein interactions, are being investigated by several strategies including deletion mutagenesis. A comparative study of five widely used PCR-based mutagenesis methods identified a modified inverse PCR method as particularly suitable for the deletion of large areas (>100 bp) in malaria parasite genes. The restriction enzyme-mediated inverse PCR method described here incorporates unique restriction enzyme sites at the 5'-ends of inverse tail-to-tail primers. The entire gene-containing vector is amplified except the desired region to be deleted and cloned using the unique restriction sites to increase ligation efficiency. This method was compared in its efficiency to delete a ~400 bp parasite-specific insert in malarial S-adenosylmethionine decarboxylase/ornithine decarboxylase (PfAdoMetDC/ODC) to existing PCR-based site-directed deletion mutagenesis methods including the QuickChange site-directed mutagenesis, ExSite, overlapping primer and inverse PCR. In addition, the modified method was applied in the deletion of a >600 bp parasite-specific insert in another malarial gene, pyridoxal kinase (PfPdxK). The modified and optimized restriction enzyme-mediated inverse PCR method resulted in 80% compared to 40% deletion mutagenesis efficiency of the overlapping primer method in the deletion of a large area (411 bp) from a large malaria gene (PfAdoMetDC/ODC, gene size 4257 bp). In contrast, deletion mutagenesis methods such as the well-known QuickChange site-directed mutagenesis, ExSite and inverse PCR methods produced insignificant results. A 100% mutagenesis efficiency was obtained with the restriction enzyme-mediated inverse PCR method to delete 618 bp from a smaller gene (PfPdxK, gene size 1536 bp). An efficient method was developed for the deletion of large areas (>100 bp) in significantly sized genes such as those of the A+T-rich P. falciparum genome.