Minus-strand RNA synthesis is guided by base-pairing between the genomic leader TRS and the copy of the body TRS present in the 3′ end of the nascent minus strand. The body TRS motifs are found preceding almost all structural genes, while a leader TRS is present at the 5′ end of the genome. There are two key elements of TRSs that are present both at the 3′ end of the leader sequence (leader TRS) and at the 5′ end of each gene in the 3′-proximal region of the genome (body TRSs). The structure of the arterivirus and coronavirus sg mRNAs derives from the discontinuous step of minus-strand RNA synthesis, which is guided by conserved AU-rich transcription-regulating sequences (TRS). The structural proteins are expressed by a nested series of subgenomic (sg) RNAs, which are produced during viral transcription. This enveloped virus bears a single-stranded, positive-sense RNA genome containing at least seven genes, encoding the replicase (ORF 1a and ORF 1b) and the structural proteins E, GP2 or GP2a, GP3, GP4, 5a, GP5, M, and N in the order 5′-ORF1-E-GP2-GP3-GP4-5a-GP5-M-N-3′. PRRSV is a member of the genus Arterivius of the family Arteriviridae within the order Nidovirales. PRRS is still one of the most economically important diseases for the swine industry worldwide. PRRS was first reported in 1987 in North America and has become pandemic within a few years. Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of porcine reproductive and respiratory syndrome (PRRS), which leads to a highly contagious respiratory disease in nursery pigs and reproductive failure in sows.
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