ALTERED PATHOGENESIS OF A MUTANT OF THE MURINE CORONAVIRUS MHV-A59 ISASSOCIATED WITH A Q159L AMINO-ACID SUBSTITUTION IN THE SPIKE PROTEIN

C12, an attenuated, fusion delayed, very weakly hepatotropic mutant of mouse hepatitis virus strain A59 (MHV-A59) has been further character ized. We have previously shown that C12 has two amino acid substitutio ns relative to wild type virus in the spike protein, Q159L (within a r egion of S1 shown to bind to viral receptor in an in vitro assay) and H716D (in the proteolytic cleavage recognition site). We have sequence d the rest of the 31-kb genome of C12 and compared it to wild type vir us. Only three additional amino acids substitutions were found, all en coded within the replicase gene. Analysis of C12 in vivo in C57Bl/6 mi ce has shown that despite the fact that this virus replicates in the b rain to titers at least as high as wild type and causes acute encephal itis similar to wild type, this virus causes a minimal level of demyel ination and only at very high levels of virus inoculation. Thus acute encephalitis is not sufficient for the induction of demyelination by M HV A59. Analysis of mutants isolated at earlier times from the same pe rsistently infected glial cell culture as C12, as well as mutants isol ated from a second independent culture of persistently infected glial cells, suggests that both the weakly demyelinating and the weakly hepa totropic phenotypes of C12 are associated with the Q159L amino acid su bstitution. (C) 1997 Academic Press.