Coronaviruses are a family of enveloped, plus-stranded RNA viruses with helical nucleocapsids and extraordinarily large genomes. The hallmark of coronavirus transcription is the production of multiple subgenomic mRNAs that contain sequences corresponding to both ends of the genome. (Transcription is defined as the process whereby subgenome-sized mRNAs are produced, and replication is the process whereby genome-sized RNA, which also functions as mRNA, is produced.) Thus, the generation of subgenomic mRNAs involves a process of discontinuous transcription. The aim of this minireview is to describe our current understanding of coronavirus replication and transcription. For more detailed information, the reader is directed to other recent reviews
CORONAVIRUS RNA REPLICATION AND TRANSCRIPTION
Model of discontinuous extension during subgenome-length minus-strand synthesis.We have proposed a model of discontinuous extension during subgenome-length minus-strand synthesis to explain the generation of coronavirus mRNAs (65) (Fig. 2). Each subgenome-length mRNA contains a 5′ leader sequence corresponding to the 5′ end of the genome. This 5′ leader is joined to a mRNA “body,” which represents sequences from the 3′-poly(A) stretch to a position that is upstream of each genomic ORF encoding a structural or niche-specific protein. The junction of the leader and body elements in each mRNA can be identified by a characteristic short, AU-rich motif of about 10 nucleotides that is known as the transcription-regulating sequence (TRS). In the genome, functional TRS motifs are found at the 3′ end of the leader (leader TRS) and in front of each ORF that is destined to become 5′ proximal in one of the subgenome-length mRNAs (body TRSs).
Our explanation of how the subgenomic mRNAs are generated has two central tenets: (i) that the process of discontinuous transcription occurs during the synthesis of minus-strand subgenome-length templates, and (ii) that the process of discontinuous transcription resembles the mechanism of similarity-assisted or high-frequency copy-choice RNA recombination.
Reference & source information:https://jvi.asm.org/
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