cyt gene of adenoviruses 2 and 5 is an oncogene for transforming function in early region E1B and encodes the E1B 19,000-molecular-weight polypeptide.

A total of 59 cytocidal (cyt) mutants were isolated from adenovirus 2 (Ad2) and Ad5. In contrast to the small plaques and adenovirus type of cytopathic effects produced by wild-type cyt+ viruses, the cyt mutants produced large plaques, and the cytopathic effect was characterized by marked cellular destruction. cyt mutants were transformation defective in established rat 3Y1 cells. cyt+ revertants and cyt+ intragenic recombinants recovered fully the transforming ability of wild-type viruses. Thus, the cyt gene is an oncogene responsible for the transforming function of Ad2 and Ad5. Genetic mapping in which we used three Ad5 deletion mutants (dl312, dl313, and dl314) as reference deletions located the cyt gene between the 3' ends of the dl314 deletion (nucleotide 1,679) and the dl313 deletion (nucleotide 3,625) in region E1B. Restriction endonuclease mapping of these recombinants suggested that the cyt gene encodes the region E1B 19,000-molecular-weight (175R) polypeptide (nucleotides 1,711 to 2,236). This was confirmed by DNA sequencing of eight different cyt mutants. One of these mutants has a single missense mutant, two mutants have double missense mutations, and five mutants have nonsense mutations. Except for one mutant, these point mutations are not located in any other known region E1B gene. We conclude that the cyt gene codes for the E1B 19,000-molecular-weight (175R) polypeptide, that this polypeptide is required for morphological transformation of rat 3Y1 cells, and that simple amino acid substitutions in the protein can be sufficient to produce the cyt phenotype.