Genetic studies with tumorigenic adenoviruses: I. Isolation of cytocidal ( cyt) mutants of adenovirus type 12

A class of cytocidal mutants, designated cyt mutants, have been isolated from two highly tumorigenic strains of adenovirus type 12 (Ad. 12), i.e., Huie and 1131. Parental viruses were plated on cell plates of low efficiency of plating, such as human amnion FL cell and human embryonic kidney (HEK) diploid cell plates. Small clear plaques, distinct from the majority of minute parental plaques, were isolated. After purification these plaques were found to be cyt mutants. Parental cyt + stocks contain approximately 0.001% spontaneous mutants recoverable by this method. Ultraviolet irradiation of cyt + stocks to 10 −1 to 10 −2 survival increases the proportion of cyt mutants by a factor of about 5. In contrast to the adenovirus-type cytopathic effect (CPE) of cyt + viruses, the CPE produced by cyt mutants is characterized by cellular destruction. The cyt mutants produce large clear plaques on HEK plates, while cyt + viruses form small fuzzy-edged plaques. Under conditions of mixed infection cyt + CPE is dominant over cyt CPE. The cyt mutants are much less tumorigenic in newborn hamsters than parental viruses and fail to transform newborn hamster kidney cells in vitro. The cyt mutants cooperate in tumorigenicity with low tumorigenic cyt + field strains as well as with Ad. 7 or Ad. 3. Thus it may be hypothesized that the cyt gene of Ad. 12 is responsible both for the production of cyt + CPE and for the tumorigenicity and may be equivalent to c 1 gene of temperate phage λ.