RNA Folding Energy of Long-Range Genomic Interactions Regulates Discontinuous Transcription in SARS-CoV-2.

Coronaviruses use discontinuous transcription to generate subgenomic RNAs (sgRNAs) that encode structural and accessory proteins. However, the factors regulating sgRNA abundance in SARS-CoV-2 remain unclear. Here, we combined strand-specific RNA sequencing, RNA-RNA interaction mapping, prediction of RNA folding energies, and targeted mutagenesis to define the regulation of (-) sgRNA synthesis in SARS-CoV-2 infection. We demonstrated that the relative (-) sgRNA abundance across viral genes is stable throughout infection and largely correlates with corresponding (+) sgmRNA levels. Through meta-analysis of published SPLASH data, we found that the frequency of long-range interactions between the 5' genomic transcription regulatory sequence TRS-Leader and downstream TRS-Body sequences correlates with sgRNA abundance. Notably, the folding energy (ΔG) of these duplexes quantitatively predicts (-) sgRNA transcript levels. Mutations in non-coding regulatory regions that altered the ΔG resulted in corresponding changes in (-) sgRNA expression, suggesting a causal role for TRS duplex stability in transcriptional regulation. Analysis of naturally occurring mutations near regulatory sites further suggests that modulation of duplex stability may also serve as an evolutionary mechanism to fine-tune viral gene expression. Together, our findings identify the pairing stability of TRS-Leader:TRS-Body as a determinant of discontinuous transcription and reveal how RNA pairing potential contributes to the regulation of (-) sgRNA synthesis in SARS-CoV-2.