The coronavirus Infectious Bronchitis Virus (IBV), a pathogen of chickens, has a genome structure typical of a coronavirus. The virus particle contains a single-stranded RNA molecule of approximately 27kb with positive polarity, and in infected cells six species of virus-specific mRNA are produced, designated RNA A to RNA F in order of increasing size (RNA F corresponding to the size of the genomic RNA). These RNAs form a nested set, in which the sequences in each of the subgenomic RNAs are also represented in all the larger RNAs; these RNA species each have a short ‘leader’ sequence corresponding to the 5′ end of the genomic RNA followed by progressively larger amounts of information derived from its 3′ -end. For each mRNA, the region of sequence which is not contained in the next smallest RNA is assumed to be used for translation of viral proteins. Polypeptide products have been assigned for RNAs A, C and E (nucleoprotein, membrane protein and the spike protein precursor respectively), but the coding function of the other RNAs has not so far been established, although it has generally been assumed that RNA F codes for the viral RNA-dependent-RNA-polymerase.
|Name||Advances in Experimental Medicine and Biology|