Transit peptides are N-terminal extensions that facilitate the targeting and translocation of cytosolically synthesized precursors into parasitic plastids, but the precise identity and mechanism of action of these peptides has been poorly understood. In the January 31 Science, Bernardo J. Foth and colleagues at the University of Melbourne, Australia, describe the transit peptides that target relict plastid (apicoplast) proteins in the malaria parasite Plasmodium falciparum (Science 299:705-708, January 31, 2003).

Foth et al. extracted amino acid features from transit peptides that target proteins to the apicoplast of P. falciparum. Based on these amino acid characteristics, they identified 466 putative apicoplast proteins in the malaria genome. They observed that altering the specific charge characteristics in a model transit peptide by site-directed mutagenesis severely disrupted organellar targeting in vivo. In addition, they showed that putative Hsp70 (DnaK) binding sites present in the transit peptide were important for...

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