Localization of a promoter in the putative internal ribosome entry site of the Saccharomyces cerevisiae TIF4631 gene

The 5′-region of the TIF4631 gene of Saccharomyces cerevisiae (encoding the translation initiation factor eIF4G1) was reported earlier to harbor a very active internal ribosome entry site (IRES) allowing for internal initiation of translation of TIF4631 mRNA. Here, we report the presence of a promoter in the region −112 to −36 relative to the translation initiation codon of the TIF4631 gene. This promoter stimulates transcription from a start site at position −36 and generates an mRNA that is actively translated in vitro and able to sustain growth of yeast cells in vivo as the only source of eIF4G. The data show that the IRES activity reported earlier is due to this promoter. On the contrary, the presumed IRES represents a strongly inhibitory element for translation in vitro.