Systematic Veterinary Virology

REPLICATION

• The replication of corona viruses is slow compared to other enveloped viruses and the viruses replicate in the cytoplasm.
• The (+) sense genome is first translated to produce a viral polymerase (RNA dep RNA Polymerase), which then produces a full-length (-) sense strand.
• This (-) sense stand is used as a template to produce mRNA as a 'nested set' of transcripts, all with an identical 5' non-translated leader sequence and coincident 3' polyadenylated ends.
• Each mRNA produced is monocistronic, the genes at the 5' end being translated from the longest mRNA and so on.
• These unusual cytoplasmic structures are produced not by splicing (post-transcriptional modification) but by the polymerase during transcription. Between each of the genes there is a repeated intergenic sequence - UCUAAAC - which interacts with the transcriptase plus cellular factors to 'splice' the leader sequence onto the start of each ORF
• Assembly occurs by budding into the golgi apparatus, particles being transported to the surface of the cell by the secretory nature of this organelle & released