Modification of carboxyl-terminal region is the cause of activation of the src gene in avian sarcoma virus S2.

Viral oncogene product of avian sarcoma virus S2 was reported to have two alterations from proto-src product; a substitution of its extreme carboxyl terminus with a peptide of helper viral protein and a point mutation which altered the 501st amino acid from arginine to lysine. However, the following data suggest that lysine501 is more common in proto-src product than arginine501. Proto-src from two independent embryos which we analyzed encoded lysine for the 501st amino acid. Rous sarcoma virus and S1, another isolate which had transduced proto-src, also coded for lysine at the same position. Thus, in the case of S2, the oncogenic activation of the src gene appeared to be achieved with only an alteration at its carboxyl terminus and enhanced expression by long terminal repeats.