Reevaluation of the conclusion that IRES-activity reported within the 5' leader of the TIF4631 gene is due to promoter activity.

We previously reported that the 5' leader of the mRNA-encoding initiation factor eIF4G in Saccharomyces cerevisiae can function as a translational enhancer and as an internal ribosome entry site (IRES) when tested in cells. However, Verge and colleagues recently suggested that this sequence does not facilitate translation initiation, but inhibits translation in vitro and has promoter activity when tested in cells. We disagree with these conclusions and respond by showing that the data are most consistent with an internal initiation mechanism.