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cDNA clones that represent various portions of the coronavirus mouse hepatitis virus strain A59 genome RNA have been constructed. cDNAs were synthesized by transcription of genome RNA by using either oligo(dT) or random oligomers of calf thymus DNA as primers. These cDNAs were converted into double-stranded DNA and cloned into pBR322 by standard techniques. The resulting cloned viral DNA fragments were mapped to viral genes by hybridization with Northern blots of intracellular RNA from mouse hepatitis virus strain A59-infected cells. These cDNA clones map in six of the seven viral genes. Clone g344, 1.8 kilobases, is the largest and encompasses gene 5 (which encodes a nonstructural protein) and gene 6 (which encodes the E1 viral glycoprotein) as well as the intergenic regions preceding genes 5, 6, and 7. Sequencing of parts of this cloned DNA show that these three intergenic regions contain a common 11-nucleotide sequence. This sequence shares homology with the 3' end of the viral mRNA leader sequence. Thus, this common intergenic sequence may contain a binding site for a leader RNA that hybridizes to negative-strand viral RNA at the beginning of each gene to prime mRNA synthesis. The different degrees of homology between the leader and its putative binding site may influence the differential rates of transcription of the various viral mRNAs.
Budzilowicz et al. (1985) studied this question.