Identification of a trypsin-like serine proteinase domain encoded by ORF 1a of the coronavirus IBV.

Abstract

Avian infectious bronchitis virus (IBV) is the prototype species of the Coronaviridae, a family of enveloped viruses with large positive-stranded RNA genomes. The genomic RNA of IBV is 27.6 kilobases (kb) in length and contains at least 10 distinct open reading frames (ORFs) (Boursnell et al., 1987). Available evidence suggests that five subgenomic mRNA species are produced in virus-infected cells. These mRNAs (mRNAs 2–6) together with the genome-length mRNA (mRNAl) range in length from about 2 kb to 27.6 kb, and have been shown to share a common 3’ -terminus and to form a nested set structure (Stern and Kennedy, 1980ab). Three of these, mRNAs 2,4 and 6, encode the major virion structural proteins spike (S), membrane (M), and nucleocapsid (N), respectively (Stern and Sefton, 1984). Two of the other mRNAs, mRNA 3 and mRNA 5, have recently been shown to encode three and two viral proteins respectively (Smith et al., 1990; Liu et al., 1991; Liu and Inglis, 1992).