Abstract

Eukaryotic translation initiation factor (eIF-5A) is a highly conserved and essential protein that contains the unique amino acid hypusine. The first step in the post-translational biosynthesis of hypusine, the transfer of an aminobutyl moiety from the polyamine substrate spermidine to the -amino group of a specific lysine residue in the eIF-5A precursor, is catalyzed by the enzyme deoxyhypusine synthase. A cDNA encoding a protein homologous to eIF-5A was isolated by plaque hybridization from a cDNA library of Plasmodium falciparum. The cloned cDNA contains an open reading frame encoding a protein of 161 amino acids, which shares a high sequence identity with other eukaryotic eIF-5A sequences. A phylogenetic tree constructed with eIF-5A from P. falciparum and 16 other eIF-5A sequences of eukaryotic and archaeal origin reveals that plasmodial eIF-5A together with other apicomplexan eIF-5A show a higher degree of homology to plant proteins than to animal and fungal sequences. The plasmodial eIF-5A gene was expressed as a six-histidine tagged fusion protein in Escherichia coli. Radioactive incorporation studies with [1,8-3H] spermidine indicated that this protein can serve as a substrate for human deoxyhypusine synthase. Results of quantitative real-time PCR studies with synchronized erythrocytic stages of P. falciparum revealed no significant induction or downregulation but only some variation in the expression level of plasmodial eIF-5A in ring, trophozoite and schizont stage.