Localization of extensive deletions in the structural genes of two neurotropic variants of murine coronavirus JHM

The intracellular RNA of two neurotropic variants of the JHM strain of mouse hepatitis virus (MHV) independently isolated from the brain and spinal cord of an infected Wistar Furth rat were compared with that of the parental virus. The mRNAs corresponding to the genes encoding the peplomer (S) and the hemagglutinin-esterase (HE) proteins of the variant viruses were found to be smaller in size. The possible sequence changes were studied by oligonucleotide fingerprinting and direct RNA sequencing. Both variants have a large deletion of 246 amino acids in the carboxy-terminal end of the HE protein. However, this truncated protein was not detected in the infected cells, suggesting either a translational regulation or rapid degradation of the truncated protein in these cells. The variant virus isolated from the spinal cord has a second deletion of 147 amino acids in the amino-terminal half of the S protein. This deletion site corresponds to a hypervariable region where deletions have been frequently noted among MHV variants with different biological properties. These findings suggest that the changes in pathogenic properties of the two neural isolates are associated with drastic alterations of the viral structural glycoproteins.