Pneumopathogenicity of a Sendai virus protease-activation mutant, TCs, which is sensitive to trypsin and chymotrypsin.

A protease-activation mutant of Sendai virus, TCs, was isolated from a trypsin-resistant mutant, TR-5. TCs was activated in vitro by both trypsin and chymotrypsin. TCs was, however, less sensitive to trypsin and chymotrypsin than were the wild-type virus and TR-5, respectively. F protein of TCs had a single amino acid substitution at residue 114 from glutamine to arginine, resulting in the appearance of the new cleavage site for trypsin and the shift of the cleavage site for chymotrypsin. Activation of TCs in the lungs of mice occurred less efficiently than that of the wild type, and TCs caused a less severe pneumopathogenicity than did the wild-type virus, which supports our previous view that the in vitro trypsin sensitivity of Sendai virus can be a good indication of pneumopathogenicity in mice.