What is an IRES sequence?
A. An IRES, or Internal Ribosomal Entry Segment, is a sequence that supports translation initiation from the second cistron in a dicistronic message. In our transfer vector pAdenoVator-CMV5-IRES-GFP or BFP, the first cistron is gene X (i.e. your favorite gene) and the second cistron is the GFP. IRES elements were first identified from the encephalomyocarditis virus messages (Ghattas et al., (1991) Mol. Cell. Biol. 11:5848-5859) but were later found in some eukaryotic messages. The secondary structure of the IRES appears to be very important for its function, more important than the sequence itself. Note that expression levels of the two genes in this dicistronic message is not equimolar; from our own experience we estimate the proportion of genes expressed to be 3:1 (1 being the gene under IRES i.e. the GFP or BFP in our construct). See reference: Mosser, D. D., A. W. Caron, et al. (1997). “Use of a dicistronic expression cassette encoding the green fluorescent protein for the screenin
