Intrinsic features of rice stripe virus cap-snatching revealed by a minimal RNP-based in vitro transcription system

Transcription of segmented negative-sense RNA viruses (sNSVs) like rice stripe virus (RSV) is initiated by cap-snatching, where the viral RNA-dependent RNA polymerase cleaves host mRNAs ~10-20 nucleotides downstream of the 5' cap to generate capped RNA leaders (CRLs) that prime viral mRNA synthesis. We previously demonstrated that purified RSV ribonucleoproteins (RNPs) support transcription <i>in vitro</i>, establishing a host-factor-free system to investigate fundamental aspects of this process. In this study, synthetic capped RNAs (scRNAs) with defined sequences were introduced into this system as CRL donors. Analysis of the resultant RSV transcripts revealed that the minimal system accurately mimics key <i>in vivo</i> features of cap-snatching. Specifically, CRL priming and realignment occurred more frequently on the viral RNA template than on the cRNA template, providing strong evidence that these processes are inherent to the viral RNP complex. Quantitative competition assays further revealed that RSV RNPs exhibit sequence-specific selectivity in cap-snatching, preferentially targeting scRNAs with adenosine or cytidine at positions 11-14, with a discernable bias towards adenosine. Surprisingly, no preference was observed for scRNAs containing AC or CA dinucleotides at the cleavage site, despite their potential to generate CRLs capable of base-pairing over two nucleotides with the viral template. Collectively, these findings offer a deeper understanding of the mechanistic aspects of RSV cap-snatching, which may also inform the study of similar processes in other sNSVs.