Pneumotropic revenants derived from a pantropic mutant, F1-R, of sendai virus

Abstract

Revenants were isolated from the protease activation mutant of Sendai virus, F1-R, which causes a systemic infection in mice. The fusion (F) glycoprotein of F1 -R is susceptible to activation cleavage by ubiquitous cellular proteases and is thus responsible for pantropism in mice (Tashiro et W., 1988. Virology 165, 577–583). The revertants regained several phenotypes of wild-type virus; they required exogenous trypsin for activation of the F protein in cell cultures and in nonpulmonary mouse tissues and they were exclusively pneurnotropic in mice. On the other hand, phenotypes of F1 -R that remained unchanged by the revenants were bipolar budding in polarized epithelial cells, enhanced electrophoretic migration of the matrix protein, and the lack of a glycosylation site in the F 2 subunit of the F protein. Comparative RNA sequence analysis of the F gene of the revertants revealed that the reduced cleavability of the F protein of the revenants was the result of the predicted single amino acid reversion (Pro to Ser) at residue 115 adjacent to the cleavage site. Thus the sequence at the cleavage site of the revenants was Ser-Lys compared with Pro-Lys for F1-R and Ser-Arg for wild-type virus. The results indicate that enhanced cleavability of the glycoprotein, a feature often associated with multiple basic residues within the cleavage site of paramyxovirus F proteins and influenza virus hemagglutinins, can also be determined by a single basic amino acid following proline. Additionally, the revenants were less susceptible to the activator for wild-type virus present in mouse lungs and less pathogenic for this organ than wild-type virus. These results provide further evidence that proteolytic activation of the F protein by host proteases is the primary determinant for organ tropism and pathogenicity of Sendai virus in mice. One of the revenants was also temperature sensitive (ts); the is lesion in the nucleoprotein gene was identical to that found in ts-f1, the is host range mutant from which F1-R was derived.