Fine structural mapping of a critical NH2-terminal region of p60src

We have recently demonstrated that an NH2-terminal sequence required for myristylation and membrane association of the Rous sarcoma virus transforming protein, p60src, is contained within amino acids 2-14 [Cross, F.R., Garber, E. A., Pellman, D. & Hanafusa, H. (1984) Mol. Cell. Biol. 4, 1834-1842]. This sequence is also required for cell transformation. We have now constructed five mutants of Rous sarcoma virus that contain alterations in the src sequence coding for these 14 amino acids. Mutants encoding src proteins with a peptide insertion between amino acids 1 and 2, or peptide substitutions for amino acids 2-4, 3-4, or 7-15, were transformation-defective. The src proteins of these mutants differed from the wild-type protein in that they were not myristylated and did not fractionate with the plasma membrane of infected cells. The fifth mutant encoded a src protein with a short peptide substituted for amino acids 11-15. This protein was myristylated and plasma membrane associated, and the virus transformed cells. We therefore conclude that a sequence required for myristylation and membrane association of p60src is located within the first 7-10 amino acids of the src protein, and that p60src myristylation and membrane association are required for cell transformation. Consistent with this idea, we have isolated four transforming revertants from one of the transformation-defective mutants. The src proteins of all four revertants were found to be myristylated and membrane associated.