Targeting the conserved stem loop 2 motif in the SARS-CoV-2 genome

RNA structural elements occur in numerous single stranded (+)-sense RNA viruses. The stem-loop 2 motif (s2m) is one such element with an unusually high degree of sequence conservation, being found in the 3' UTR in the genomes of many astroviruses, some picornaviruses and noroviruses, and a variety of coronaviruses, including SARS-CoV and SARS-CoV-2. The evolutionary conservation and its occurrence in all viral subgenomic transcripts implicates a key role of s2m in the viral infection cycle. Our findings indicate that the element, while stably folded, can nonetheless be invaded and remodelled spontaneously by antisense oligonucleotides (ASOs) that initiate pairing in exposed loops and trigger efficient sequence-specific RNA cleavage in reporter assays. ASOs also act to inhibit replication in an astrovirus replicon model system in a sequence-specific, dose-dependent manner and inhibit SARS-CoV-2 replication in cell culture. Our results thus permit us to suggest that the s2m element is readily targeted by ASOs, which show promise as anti-viral agents.IMPORTANCEThe highly conserved stem-loop 2 motif (s2m) is found in the genomes of many RNA viruses including SARS-CoV-2. Our findings indicate that the s2m element can be targeted by antisense oligonucleotides. The anti-viral potential of this conserved element represents a promising start for further research into targeting conserved elements in RNA viruses.