Transformation by p60src with altered N-terminal sequences.

The transforming activity of the src gene product of Rous sarcoma virus, p60src, depends on both tyrosine specific protein kinase activity and N-terminal myristylation that is required for the plasma membrane association of this protein. The src proteins of two recovered avian sarcoma viruses, rASV157 and rASV1702, are exceptional in that they are not myristylated and yet are active in transformation. These viruses also induce tumors that regress rapidly. We found that their src proteins have unusual N-terminal structures: 30-45 amino acids of the env signal peptide are attached to internal (6th and 76th) amino acids in the src sequences. These altered N-terminal structures seem to be responsible for many abnormal properties of these mutant src proteins, including the early regression of tumors they induce.