Myristic acid, a rare fatty acid, is the lipid attached to the transforming protein of Rous sarcoma virus and its cellular homolog.

The lipid bound to p60src, the transforming protein of Rous sarcoma virus, has been identified by gas and thin-layer chromatography as the 14-carbon saturated fatty acid, myristic acid. The protein can be labeled biosynthetically with either 3H]myristic acid or 3H]palmitic acid. Incorporation of 3H]myristic acid was noticeably greater than incorporation of 3H]palmitic acid. All of the 3H]myristic acid-derived label in p60src was present as myristic acid. In contrast, none of the radioactivity derived from 3H]palmitic acid was recovered as palmitic acid. Instead, all 3H incorporated into p60src from 3H]palmitic acid arose by metabolism to myristic acid. The cellular tyrosine kinase, p60c-src also contains myristic acid. By comparison of the extent of myristylation of p60v-src with that of the Moloney murine leukemia virus structural protein precursor, Pr65gag, we estimate that greater than 80% of the molecules of p60v-src contain one molecule of this fatty acid. Myristylation is a rare form of protein modification. p60v-src contains 10 to 40% of the myristic acid bound to protein in cells transformed by Rous sarcoma virus and is easily identified in total cell lysates when 3H]myristic acid-labeled proteins are separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Comparison of the amount of 3H]myristic acid-labeled p60src in total cell lysates and in immunoprecipitates suggests that immunoprecipitation with rabbit anti-Rous sarcoma virus tumor sera detects ca. 25% of the p60src present in cells.