SUMMARY

A coding sequence at the 5 ' end of mRNA 4 of the coronavirus MHV-JHM was determined by M13/chain-terminator sequencing of cloned cDNA. An open reading frame of 417 bases with the potential to encode a polypeptide of mol. wt. 15200 (139 residues) was identified. The 3 ' end of the open reading frame overlapped by 16 bases the start of an open reading frame found in mRNA 5. The translation product of mRNA 4 was predicted to be a basic polypeptide rich in threonine. It had a large hydrophobic region near the amino terminus and a basic carboxy terminus. An intracellular, virus-specific polypeptide, which has been previously described as having a mol. wt. of 14000 to 14500 has the size and charge characteristics of such a translation product. Murine hepatitis virus (MHV) is a member of the Coronaviridae which are cytoplasmic, enveloped, RNA viruses, The molecular biology of this virus group has been reviewed recently (Siddell et al., 1983). Briefly, in cells infected by MHV, in addition to the genomic RNA (tool. wt. 6.0 x 106), six subgenomic mRNAs with mol. wt. ranging from 0.6 x 106 to 3.7 × 106 are produced. The genomic-size RNA which is infectious is termed mRNA 1 and the smalles