Fig. 7.

Coronavirus transcription. Representation of the coronavirus discontinuous transcription during negative-strand synthesis. Transcription regulating sequences from the leader (TRS-L) and preceding a gene (TRS-B) are shown in yellow. Negative polarity RNA synthesis begins from 3′-end of the coronavirus genome. Once the transcription complex copies the TRS-B template switch of the nascent RNA to the leader sequence (red) takes place and the sequence complementary to the TRS-B (cTRS-B) hybridizes with the TRS-L. This process is indicated by the dark red arrow. Nascent RNA synthesis continues with the copy of the leader sequence (red), leading to a negative polarity subgenomic RNA (sg RNA) that will be used as a template for the generation of the sg mRNAs of positive polarity. Genomic RNA and sg mRNA strands are shown in dark colors. Negative polarity RNA strands are shown in light colors.