Figure 1.

Nucleotide metabolism in G. intestinalis. The parasite lacks many pathways in nucleotide metabolism including ribonucleotide reductase (RNR) and thymidylate synthase (TS), which are crucial for general dNTP synthesis and dTTP synthesis, respectively. Consequently, the parasite is completely dependent on deoxyribonucleoside kinases to make dNTPs. There are three such kinases in the G. intestinalis WB genome, including two deoxyribonucleoside kinases from the dCK-dGK-TK2 family (dNKs, ORFs 4558 and 17451) and one from the thymidine kinase 1 family (TK, ORF 8364).