Complete sequence (20 kilobases) of the polyprotein-encoding gene 1 of transmissible gastroenteritis virus

The entire nucleotide sequence of cloned cDNAs containing the 5'-untranslated region and gene 1 of Purdue-115 strain of transmissible gastroenteritis virus (TGEV) was determined. This completes the sequence of the TGEV genome, which is 28,579 nucleotides long. The gene 1 is composed of two large open reading frames, ORF1a and ORF1b, which contain 4017 and 2698 codons, respectively (stop excluded). A brief, three-codon-long ORF is present upstream of ORF1a. ORF1b overlaps ORF1a by 43 bases in the (-1) reading frame. In vitro experiments indicated that translation of the ORF1a/b polyprotein involves an efficient ribosomal frameshifting activity, as previously shown for other coronaviruses. Analysis of the predicted ORF1a and ORF1b translation products revealed that the putative functional domains identified in infectious bronchitis virus (IBV), mouse hepatitis virus (MHV) and human coronavirus 229E (HCV 229E) are all present in TGEV. The amino-terminal half of the ORF1a product exhibits greater divergence than the carboxyl-terminal half, including within the TGEV/HCV229E pair. The ORF1b protein is overall highly conserved among the above four coronaviruses, except a divergent region situated near the carboxy terminus.