CLONING, SEQUENCE DETERMINATION, AND REGULATION OF THE RIBONUCLEOTIDEREDUCTASE SUBUNITS FROM PLASMODIUM-FALCIPARUM - A TARGET FOR ANTIMALARIAL THERAPY

Malaria remains a leading cause of morbidity and mortality worldwide, accounting for more than one million deaths annually. We have focused on the reduction of ribonucleotides to 2'-deoxyribonucleotides, cataly zed by ribonucleotide reductase, which represents the rate-determining step in DNA replication as a target for antimalarial agents. We repor t the full-length DNA sequence corresponding to the large (PfR1) and s mall (PfR2) subunits of Plasmodium falciparum ribonucleotide reductase . The small subunit (PfR2) contains the major catalytic motif consisti ng of a tyrosyl radical and a dinuclear Fe site. Whereas PfR2 shares 5 9% amino acid identity with human R2, a striking sequence divergence b etween human R2 and PfR2 at the C terminus may provide a selective tar get for inhibition of the malarial enzyme. A synthetic oligopeptide co rresponding to the C-terminal 7 residues of PfR2 inhibits mammalian ri bonucleotide reductase at concentrations almost-equal-to 10-fold highe r than that predicted to inhibit malarial R2. The gene encoding the la rge subunit (PfR1) contains a single intron. The cysteines thought to be involved in the reduction mechanism are conserved. In contrast to m ammalian ribonucleotide reductase, the genes for PfR1 and PfR2 are loc ated on the same chromosome and the accumulation of mRNAs for the two subunits follow different temporal patterns during the cell cycle.