The efficiency of different IRESs (Internal ribosomes entry site) in monocistronic mRNAS

The IRES from poliovirus and from encephalomyocarditis virus (EMCV) added b etween the cap and the AUG initiator codon were strong inhibitors of chlora mphenicol acetyltransferase gene expression in three different cell types. The poliovirus IRES also inhibited bGH (bovine growth hormone) cDNA express ion in the HC11 mammary cell line when added between the rabbit whey acidic gene promoter and the cDNA whereas the HTLV-1 IRES showed a stimulatory ef fect in the same situation. RNA stem loops were added before HTLV-1 (SUR) a nd the BiP (Immunoglobulin heavy-chain Binding Protein) IRESs followed by t he firefly luciferase gene under the control of Rous sarcoma virus (RSV) pr omoter. The RNA loops abolished the expression of the reporter gene almost completely. These data suggest that the different IRESs may favour or inhib it translation of monocistronic mRNA.