Plasmids used to assay termination-reinitiation were based on the p2luc reporter vector [20] . Sequences encompassing the stopstart signal of MNV (203 bp of sequence information upstream of the VP1 stop codon and 52 bp downstream) and FCV (97 bp upstream of the VP1 stop codon and 14 bp downstream) were generated by PCR (using Pfu polymerase [Roche]) from, respectively, plasmids pT7:MNV (kind gift of Dr Ian Goodfellow, Imperial College, London) and pSG-2/3* [13] , a kind gift of Dr Tuiya Pöyry, University of Cambridge. The PCR products and p2luc were digested with SalI and BamHI and ligated together. Sequences were confirmed by dideoxy sequencing (using the facility at the Department of Biochemistry, University of Cambridge). The influenza B termination-reinitiation assay plasmid (p2luc-BM2wt; 250 bp upstream of M1 stop-codon, 18 bp downstream) was described previously [19] .