The thermal inactivation of T4 and lambda bacteriophage.

Thermal inactivation of T(4) and lambda bacteriophage shows two components of differing sensitivity are present. These cannot be interpreted as owing to nucleic acid and protein. One protein function-the inhibition of radiation-induced DNA degradation-is lost with quite different thermal kinetics. lambda heated in the presence of DNase is more rapidly inactivated; lambda is also protected by slow cooling after heat. These results suggest that the packing of the DNA in the head occurs so as to permit different degrees of thermal expansion in the outer coils. These can rupture the coat and this is one form of inactivation. Killed vaccines could be more safely made by heating in the presence of a nuclease followed by rapid cooling.