Posttranslational modification of the Ha-ras oncogene protein: evidence for a third class of protein carboxyl methyltransferases.
The ras oncogene products require membrane localization for their function, and this is thought to be accomplished by the addition of a palmitoyl group to a cysteine residue near the carboxyl terminus of the nascent chain. A lipidated carboxyl-terminal cysteine residue is also found in sequence-related yeast sex factors, and in at least two cases, the alpha-carboxyl group is also methyl esterified. To determine if ras proteins are themselves modified by a similar type of methylation reaction, we incubated rat embryo fibroblasts transformed with p53 and activated Ha-ras oncogenes with L-[methyl-3H]methionine under conditions in which the isotope was converted to the methyl donor S-adenosyl-L-[methyl-3H]methionine. By using an assay that detects methyl ester linkages, we found that immunoprecipitated ras proteins are in fact esterified and that the stability of these esters is consistent with a carboxyl-terminal localization. This methylation reaction may be important in regulating the interaction of ras proteins with plasma membrane components. The presence of analogous carboxyl-terminal tetrapeptide sequences in other proteins may provide a general recognition sequence for lipidation and methylation modification reactions.
Clarke
S
S
Department of Molecular Biology, Princeton University, NJ 08544.
Vogel
J P
JP
Deschenes
R J
RJ
Stock
J
J
D000818:Animals; D002471:Cell Transformation, Neoplastic; D005347:Fibroblasts / Q000378:metabolism; D009363:Neoplasm Proteins / Q000096:biosynthesis; D010750:Phosphoproteins; D011496:Protein Methyltransferases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D016283:Proto-Oncogene Proteins p21(ras); D051381:Rats; D012436:S-Adenosylmethionine / Q000378:metabolism; D016159:Tumor Suppressor Protein p53
D009363:Neoplasm Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D012436:S-Adenosylmethionine; D011496:Protein Methyltransferases; C056501:protein-S-isoprenylcysteine O-methyltransferase; D016283:Proto-Oncogene Proteins p21(ras)