Proline 137 Is Critical for Adenovirus Protease Encapsidation and Activation but Not Enzyme Activity

Abstract

Infection with the adenovirus type 2 ts1 mutant at the nonpermissive temperature resulted in the production of noninfectious virions. This has been ascribed to the P137L mutation in the virus-encoded cysteine protease which causes a defect in protease activity. Here we have examined the ts1 defect in detail as a means of learning more about the viral protease. The ts1 protease accumulated in the nucleus normally and was found associated with incomplete particles as was the case with wt. This enzyme was active in both wt and ts1 incomplete particles produced at 39° (ts1-39 TCs), provided they were dissociated with 4 M urea. While the wt protease was packaged into complete particles, the ts1-39 particles were totally devoid of protease. This defect was nearly completely corrected by addition of the 11-residue activating peptide PVIc (GVQSLKRRRCF) to the medium late in infection. Rescue of ts1 occurred via restoration of enzyme activity and packaging of the ts1 enzyme into complete virions. Recombinant ts1 enzyme was not temperature sensitive. The P137L mutation responsible for the ts1 defect appeared therefore to be an in vivo phenotype involving apparently linked events of protease packaging and activation mediated by the PVI protein.