The causative agent of malaria, Plasmodium, possesses three translationally 
active compartments: the cytosol, the mitochondrion and a relic plastid called 
the apicoplast. Aminoacyl-tRNA synthetases to charge tRNA are thus required for 
all three compartments. However, the Plasmodiumfalciparum genome encodes too few 
tRNA synthetases to supply a unique enzyme for each amino acid in all three 
compartments. We have investigated the subcellular localisation of three tRNA 
synthetases (AlaRS, GlyRS and ThrRS), which occur only once in the nuclear 
genome, and we show that each of these enzymes is dually localised to the P. 
falciparum cytosol and the apicoplast. No mitochondrial fraction is apparent for 
these three enzymes, which suggests that the Plasmodium mitochondrion lacks at 
least these three tRNA synthetases. The unique Plasmodium ThrRS is the presumed 
target of the antimalarial compound borrelidin. Borrelidin kills P. falciparum 
parasites quickly without the delayed death effect typical of apicoplast 
translation inhibitors and without an observable effect on apicoplast 
morphology. By contrast, mupirocin, an inhibitor of the apicoplast IleRS, kills 
with a delayed death effect that inhibits apicoplast growth and division. 
Because inhibition of dual targeted tRNA synthetases should arrest translation 
in all compartments of the parasite, these enzymes deserve further investigation 
as potential targets for antimalarial drug development.