Cloning and expression of a cDNA encoding the alpha subunit of rat p21ras protein farnesyltransferase

The complete amino acid sequence of the alpha subunit of heterodimeric p21ras protein farnesyltransferase from rat has been deduced from the sequence of a cloned cDNA. The cDNA encodes a 377-amino acid protein that migrates on NaDodSO4/polyacrylamide gels identically to the alpha subunit purified from rat brain. When introduced into mammalian cells by transfection, the cDNA for the alpha subunit produced no immunodetectable protein or farnesyltransferase activity unless the cells were simultaneously transfected with a cDNA encoding beta subunit. In light of previous evidence that alpha subunit forms a heterodimer with at least two different beta subunits, current data suggest a mechanism for coordinating amounts of alpha and beta subunits. If an alpha subunit were stable only as a complex with a beta subunit, the number of alpha subunits would be automatically maintained at a level just sufficient to balance all beta subunits, thereby avoiding the potentially toxic overaccumulation of free alpha subunits.