The CrPV-p2luc-BM2 plasmid series was generated by digestion of p2luc-BM2wt with PstI and NheI, and insertion of a PCR fragment comprising the cricket paralysis virus (CrPV) IRES downstream of a bacteriophage T7 promoter. The T7-CrPV fragment was generated by PCR from plasmid CrPV/+8norm [14] . The resulting plasmid contains a T7 promoter located 25 nt upstream of the CrPV IRES. Translation starts on an alanine codon within the inserted CrPV fragment, resulting in an Nterminal extension to rluc of 10 amino acids relative to that of the p2luc-BM2wt. Derivative plasmids were generated by site-directed mutagenesis using primers described previously [11] .