Internal Ribosome Entry Site - Testing

Testing

Testing a particular RNA sequence for IRES activity relies on a bicistronic reporter construct. When an IRES segment is located between two reporter open reading frames in a eukaryotic mRNA molecule (a bicistronic mRNA), it can drive translation of the downstream protein coding region independently of the 5'-cap structure bound to the 5' end of the mRNA molecule. In such a setup both proteins are produced in the cell. The first reporter protein located in the first cistron is synthesized by the cap-dependent initiation approach while translation initiation of the second protein is directed by the IRES segment located in the intercistronic spacer region between the two reporter protein coding regions. However, there are several caveats to be aware of when interpreting data produced using bicistronic reporter constructs. For example, there are several known cases of mis-reported IRES segments that were later recognized as promoter-containing regions. More recently, splice acceptor sites within several presumed IRES segments have been shown to be responsible for apparent IRES function in bicistronic reporter assays.