Binding and repression of translation of the cognate mRNA by Trichinella spiralis thymidylate synthase differ from the corresponding interactions of the human enzyme

摘要

pThymidylate synthase (TS) of iTrichinella spiralis/i, a parasitic nematode causing trichinellosis, was found to bind its own mRNA and repress translation of the latter, similar to its human counter-part [Chu, Koeller, Casey, Drake, Chabner, Elwood, Zinn and Allegra (1991) Proc. Natl. Acad. Sci. U.S.A. b88/b, 8977–8981]. However, in striking contrast with human TS, the parasite enzyme9s interaction with mRNA was not affected by any of the substrate (deoxyuridylate or iN/isup5,10/sup-methylenetetrahydrofolate) nor by the inhibitor (fluorodeoxyuridylate; used alone or in the presence of iN/isup5,10/sup-methylenetetrahydrofolate) similar to that shown for the bifunctional enzyme from iPlasmodium falciparum/i [Zhang and Rathod (2002) Science b296/b, 545–547]. Moreover, repression of the translation of the parasite enzyme was enhanced by the same ligands that were shown by others (Chu et al., 1991) to prevent human TS from impairing its translation. On comparing the capacity of TS to bind to its cognate mRNA, relative to its ability to inhibit its translation, the same enzyme preparation was active as translational repressor at a considerably lower protein/mRNA ratio, suggesting the two phenomena to be disconnected. Of interest is the fact that the presence of the enzyme protein N-terminal methionine proved to be critical for binding, but not for repression of its translation, indicating that mRNA binding requires a methionine or an adduct (i.e. methionine–histidine) at the N-terminus of TS, but that the translational repression effect does not. Notably, chicken liver dihydrofolate reductase, which is incapable of binding to iT. spiralis/i TS mRNA, repressed the translation of TS./p