Fig. 2

RSV performs transcription in vitro. a A diagram illustrating the strategy to detect in vitro transcripts (the NP mRNA). CMV RNAs (the blue line, only one of the CMV RNA segments was shown here) and RSV RNPs are present in the reaction mixture. The RdRp (red ball) of RSV RNPs (only one RNP is shown here) cleaves CMV RNAs, obtaining a CRL (not shown). The CRL is used as a primer to transcribe viral template RNAs, leading to the generation of chimeric RSV mRNAs with a CMV-derived CRL at their 5ʹ ends, which can be detected by nested RT-PCR using primers 1, 2 and 3 (P1–P3). Primer 2 is a composite primer with ten nucleotides at its 3ʹ-end identical to the 5ʹ terminus of CMV RNA1. Similar nested RT-PCR was conducted to detect RSV and CMV genomic RNAs. In doing this, all the three primers anneal to the coding region of RSV NP (not shown) or CMV RNA1. b Gel electrophoresis of the RT-PCR product. The RT-PCR product from each reaction mixture as indicated on top of the gel was electrophoresed in a 1.5% agarose gel before being visualized