Several lines of evidence demonstrated that organisms ranging from bacteria to higher animals possess a regulated endonucleolytic cleavage pathway producing half-
tRNA fragments. In the present study, we investigated the occurrence of this phenomenon in two distantly related apicomplexan parasites, Toxoplasma gondii, the agent of
toxoplasmosis, and the rodent
malaria parasite Plasmodium berghei. A low-scale molecular characterization of the small
RNA fraction of T. gondii revealed the endonucleolytic processing of 10 distinct
tRNA species, with cleavage in the
anticodon loop and upstream of the 3'-terminal CCA sequence yielding 5'- or 3'-end half-tRNAs. T. gondii and P. berghei exhibited variable rates of
tRNA cleavage upon egress from host cells and in response to stage differentiation,
amino acid starvation and heat-shock. Moreover, avirulent isolates of T. gondii and attenuated P. berghei parasites showed a higher rate of
tRNA cleavage than virulent strains. Interestingly, half-
tRNA production was significantly higher in the metabolically quiescent bradyzoite and sporozoite stages of T. gondii, compared to the fast-growing tachyzoite. Collectively, our findings shed light for the first time on the occurrence of
tRNA cleavage in apicomplexan parasites and suggest a relationship between half-
tRNA production and growth rate in this important group of organisms.