In vitro synthesis of two polypeptides from a nonstructural gene of coronavirus mouse hepatitis virus strain A59

The complete nucleotide sequence of nonstructural gene 5 of coronavirus mouse hepatitis virus (MHV) strain A59 has been determined. This sequence contains two potential open reading frames which overlap by five nucleotides. The putative protein products predicted from the sequence are a basic 13,000-Da polypeptide and a 9600-Da polypeptide containing an unusually long hydrophobic amino terminus. RNAs transcribed in vitro from DNAs containing each of the open reading frames in pGEM vectors direct the synthesis in vitro of polypeptides of the sizes predicted by the sequence. An RNA transcript containing both of the open reading frames directs the synthesis primarily of the polypeptide corresponding to the downstream open reading frame. These data suggest that MHV-A59 messenger RNA 5 potentially encodes two proteins and may be preferentially translated from an internal AUG initiation codon.