A CONDITIONAL-LETHAL MURINE CORONAVIRUS MUTANT THAT FAILS TO INCORPORATE THE SPIKE GLYCOPROTEIN INTO ASSEMBLED VIRIONS

The coronavirus spike glycoprotein (S) mediates both the attachment of virus to the host cell receptor and membrane fusion. We describe here the characterization of a temperature-sensitive mutant of the coronav irus mouse hepatitis virus A59 (MHV-A59) having multiple S protein-rel ated defects. The most remarkable of these was that the mutant, design ated Albany 18 (Alb18), assembled virions devoid of the S glycoprotein at the nonpermissive temperature. Alb18 also failed to bring about sy ncytia formation in cells infected at the nonpermissive temperature. V irions of the mutant assembled at the permissive temperature were much more thermolabile than wild type. Moreover, mutant S protein that was incorporated into virions at the permissive temperature showed enhanc ed pH-dependent thermolability in its ability to bind to the MHV recep tor. Alb18 was found to have a single point mutation in S resulting in a change of serine 287 to isoleucine, and it was shown by revertant a nalysis that this was the lesion responsible for the phenotype of the mutant.