Hsp70 genes encode abundant heat-inducible 70-kDa hsps (hsp70s). In most eukaryotes hsp70 genes exist as part ofa multigene family. They are found in most cellularcompartments of eukaryotes including nuclei,mitochondria, chloroplasts, the endoplasmic reticulumand the cytosol, as well as in bacteria. The genes show ahigh degree of conservation, having at least 5O% identity(1). The N-terminal two thirds of hsp70s are moreconserved than the C-terminal third. Hsp70 binds ATPwith high affinity and possesses a weak ATPase activitywhich can be stimulated by binding to unfolded proteinsand synthetic peptides (2). When hsc70 (constitutivelyexpressed) present in mammalian cells was truncated, ATPbinding activity was found to reside in an N-terminal fragmentof 44 kDa which lacked peptide binding capacity. Polypeptidebinding ability therefore resided within the C-terminal half(3). The structure of this ATP binding domain displays multiplefeatures of nucleotide binding proteins (4).All hsp70s, regardless of location, bind proteins, particularlyunfolded ones. The molecular chaperones of the hsp70 familyrecognize and bind to nascent polypeptide chains as well aspartially folded intermediates of proteins preventing theiraggregation and misfolding. The binding of ATP triggers acritical conformational change leading to the release of thebound substrate protein (5). The universal ability of hsp70s toundergo cycles of binding to and release from hydrophobicstretches of partially unfolded proteins determines their rolein a great variety of vital intracellular functions such asprotein synthesis, protein folding and oligomerization andprotein transport.PfHsp70-I (PF08_0054) is the major cytosolic Hsp70 inPlasmodium falciparum. It is abundantly expressed in theblood stages of the parasite and is thought to constitute 1-2%of total parasite protein. It is induced upon heat shock. It ispresent in the parasite in different complexes with PfHsp90and some PfHsp40 (6, 7).