The biochemical composition of coronavirus Nucleocapsid proteins drives the bicistronic properties of their sub-genomic mRNAs

Frame 2 of the nucleocapsid gene in Alpha-, Beta-, and Delta-coronaviruses frequently contains a conserved potential accessory ORF, unlike spike, envelope, and membrane genes.

• Why it matters: Dual coding in coronavirus sub-genomic mRNAs is known for SARS- and MERS-CoV, but its prevalence across the coronavirus family and the sequence features enabling overlapping ORFs were unclear.
• What they did: The ORFan in-silico tool screened sub-genomic mRNA sequences from 152 coronavirus species for overlapping accessory gene candidates, then linked frame-specific start/stop abundance to nucleotide and codon biases tied to N protein RNA-binding function.
• The result: The combined bias model explains the tendency toward frame 2 AcORFs and suggests that similar nucleotide and codon constraints may facilitate overlapping ORF formation in other virus families.

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