Forty years with coronaviruses

Weiss, Susan R.

During the 1980s, several important findings were reported. The coronavirus genomic RNA is transcribed into a set of subgenomic mRNAs that encode viral proteins. Using the model MHV, these subgenomic RNAs were shown to each contain a leader sequence derived from the 59 end of the genome (Lai et al., 1982) , initially by RNA fingerprinting methods. These nested subgenomic RNAs came to define a larger superfamily of Nidoviruses ("nidus" means nest) including several other virus families. Later it was found that subgenomic mRNAs are transcribed from negative strand RNAs that were synthesized from the full-length genomic RNA (Wu and Brian, 2010) . This is a unique mechanism involving noncontiguous transcription of the genome, presumed to occur by a process involving viral polymerase jumping from one part of the genome template to another. This leads to a high rate of recombination for coronaviruses, which may play a role in viral evolution and interspecies infections. However, the ancestral bat virus of SARS-CoV-2, the species from which it was transferred to humans, and the sequence changes leading to the evolution of this highly pathogenic virus have yet to be identified.