The solution structure of coronaviral stem-loop 2 (SL2) reveals a canonical CUYG tetraloop fold

The transcription and replication of the severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) is regulated by specific viral genome sequences within 5′- and 3′-untranslated regions (5′-UTR and 3′-UTR). Here we report the solution structure of 5′-UTR derived stem-loop 2 (SL2) of SARS-CoV determined by NMR spectroscopy. The highly conserved pentaloop of SL2 is stacked on 5-bp stem and adopts a canonical CUYG tetraloop fold with the 3′ nucleotide (U51) flipped out of the stack. The significance of this structure in the context of a previous mutagenesis analysis of SL2 function in replication of the related group 2 coronavirus, mouse hepatitis virus, is discussed.