FIG. 6.

Thermal inactivation of mutant 3 (Alb154: K63A, K67A), mutant 4 (Alb183: D60A, R61A, K63A), and the isogenic wild-type strain (Alb129). (A) Passage 3 stocks of each virus were grown at 33°C and thermally inactivated at 40°C (pH 6.5) for the indicated times (22). Titers of surviving viruses were determined at 37°C. (B) Same as panel A but with virus stocks grown at 39°C. The titers of virus stocks prior to heat treatment are indicated at the bottom.