Malaria remains a public health problem of enormous magnitude, affecting over 500 million people every year. Lack of success in the past in the development of new
drug/
vaccines has mainly been attributed to poor understanding of the functions of different parasite
proteins. Recently, RNA interference (RNAi) has emerged as a simple and incisive technique to study gene functions in a variety of organisms. In this study, we report the results of RNAi by
double-stranded RNA of
cysteine protease genes (falcipain-1 and -2) in the
malaria parasite, Plasmodium falciparum. Using RNAi directed towards
falcipain genes, we demonstrate that blocking the expression of these genes results in severe morphological abnormalities in parasites, inhibition of parasite growth in vitro and substantial accumulation of haemoglobin in the parasite. The inhibitory effects produced by
falcipain double-stranded (ds)RNAs are reminiscent of the effects observed upon administering
E-64, a
cysteine protease inhibitor. The parasites treated with
falcipain's dsRNAs also show marked reduction in the levels of corresponding endogenous
falcipain mRNAs. We also demonstrate that dsRNAs of falcipains are broken into short interference RNAs approximately 25
nucleotides in size, a characteristic of RNAi, which in turn activates sequence-specific nuclease activity in the
malaria parasites. These results thus provide more evidence for the existence of RNAi in P. falciparum and also suggest possibilities for using RNAi as an effective tool to determine the functions of the genes identified from the P. falciparum genome sequencing project.