Inactivation of expression of gene 4 of mouse hepatitis virus strain JHM does not affect virulence in the murine CNS

The protein encoded by ORF 4 of mouse hepatitis virus (MHV) is not required for growth of some strains in tissue culture cells, but its role in pathog enesis in the murine host has not been defined previously in a controlled m anner. MHV strain JHM causes acute and chronic neurological diseases in sus ceptible strains of rodents. To genetically manipulate the structural prote ins of this and other strains of MHV, we have generalized an interspecies-t argeted RNA recombination selection that was originally developed for the A 59 strain of MHV. Using this approach, a recombinant MHV-JHM was constructe d in which gene 4 was genetically inactivated. Virus lacking gene 4 express ion replicated in tissue culture cells with similar kinetics to recombinant virus in which gene 4 expression was not disrupted. Both types of viruses exhibited similar virulence when analyzed in a murine model of encephalitis . These results establish a targeted recombination system for inserting mut ations into MHV-JHM. Furthermore, the protein encoded by ORF 4 is not essen tial for growth in tissue culture cells or in the CNS of the infected host. (C) 2001 Academic Press.