Hybridization arrest of cell-free translation of the malarial dihydrofolate reductase/thymidylate synthase mRNA by anti-sense oligodeoxyribonucleotides.

In order to inhibit the in vitro translation of Plasmodium falciparum mRNA coding for the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS), oligodeoxynucleotides (ODNs) were directed against the translation initiation site or a site in the TS-coding region. In both cases considerable hybridization arrest, i.e. greater than 50% inhibition, was only achieved if the lengths of the ODNs to the two regions were 30 and 39 nucleotides, respectively, or longer. The ODN with the highest efficiency was a 49-mer directed against the TS-coding region (OTS49); 45 microM was sufficient to inhibit the expression of DHFR-TS by almost 90%. In this case the synthesis of DHFR-TS was interrupted at the binding site of OTS49 by a RNase H-independent mechanism. The resulting polypeptide was smaller (55 kDa) than one subunit of the native protein (71 kDa) and lacked TS activity.