The strand-biased transcription of SARS-CoV-2 and unbalanced inhibition by remdesivir.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive single-stranded RNA virus, causes the coronavirus disease 19 pandemic. During the viral replication and transcription, the RNA-dependent RNA polymerase "jumps" along the genome template, resulting in discontinuous negative-stranded transcripts. Although the sense-mRNA architectures of SARS-CoV-2 were reported, its negative strand was unexplored. Here, we deeply sequenced both strands of RNA and found SARS-CoV-2 transcription is strongly biased to form the sense strand with variable transcription efficiency for different genes. During negative strand synthesis, numerous non-canonical fusion transcripts are also formed, driven by 3-15 nt sequence homology scattered along the genome but more prone to be inhibited by SARS-CoV-2 RNA polymerase inhibitor remdesivir. The drug also represses more of the negative than the positive strand synthesis as supported by a mathematic simulation model and experimental quantifications. Overall, this study opens new sights into SARS-CoV-2 biogenesis and may facilitate the antiviral vaccine development and drug design.