Purified virions (1.4 × 10 11 ) were incubated with 25 µg/ ml of purified neutrophil elastase (Calbiochem) in 40 µL of VDB at 37°C for 3 h. Reactions were terminated by adding 1 mM PMSF and 200 µM NE inhibitor to the reaction mixture. 5.0 × 10 10 particles were run on SDS-12% polyacrylamide gels stained with Coomassie Brilliant Blue to confirm the removal of σ3. Viral infectivity was determined by plaque assay on L929 cell monlayers.