Isoprenylated proteins function in important regulatory roles in various cellular processes. Selective inhibition of protein prenylation has been shown to be useful in the control of cell division and differentiation in targeted cells. Little is known about the role of isoprenylation or types of protein prenyl transferases in Plasmodium falciparum. Our hypothesis is that biochemical characterization of protein prenyltransferases from P. falciparum is important for the elucidation of key regulatory components of the signaling pathways of this organism and that studies of the sensitivity of these enzymes to inhibitors will determine whether these enzymes could serve as potential targets for antimalarials. This proposal aims to purify and characterize two types of P. falciparum protein prenyltransferases: protein farnesyl transferase (PFT) and protein geranylgeranyltransferase (PGGT-I). Additional aims are to test the sensitivity of P. falciparum growth and prenyltransferase activity to substrate related inhibitors and to identify physiological substrates for the P. falciparum PFT. The specific aims are 1) to clone the alpha- and beta-subunits of P. falciparum PFT and overexpress them in E. coli or baculovirus, 2) to purify catalytically active recombinant PFT by peptide-affinity chromatography and characterize its subunit composition, 3) to purify native P. falciparum PFT and PGGT-I enzymes to the highest degree possible and compare them with respect to their subunit composition, 4) to characterize and compare recombinant PFT, native PFT and PGGT-I enzymes with respect to their substrate specificity and kinetic properties, 5) to test prodrug peptidomimetic compounds and other derivatives as inhibitors of cell division and growth of P. falciparum, 6) to test peptidomimetics and other prenyltransferase inhibitors as in vitro inhibitors of the PFTs and PGGT-Is, and 7) to identify physiological substrates for P. falciparum PFT by co-immunprecipitation, by identifying peptide sequences interacting with PFT subunits using a phage phage display peptide library and by expression cloning.