The mechanism of synthesis of ornithine decarboxylase (ODC) at the level of translation was studied using cell culture and cell-free systems. Synthesis of firefly luciferase (Flue) from the second open reading frame (ORF) in a bicistronic construct transfected into FM3A and HeLa cells was enhanced by the presence of the 5'-untranslated region (5'-UTR) of ODC mRNA between the two ORFs. However, cotransfection of the gene encoding 2A protease inhibited the synthesis of Flue. Synthesis of Flue from the second cistron in the bicistronic mRNA in a cell-free system was not affected significantly by the 5'-UTR of ODC mRNA. Synthesis of ODC from ODC mRNA in a cell-free system was inhibited by 2A protease and cap analogue (M(7)GpppG). Rapamycin inhibited ODC synthesis by 40-50% at both the G(1)/S boundary and the G(2)/M phase. These results indicate that an IRES in the 5'-UTR of ODC mRNA does not function effectively. (C) 2007 Elsevier Inc. All rights reserved.