cDNA cloning and expression of the peptide-binding β subunit of rat p21^rasfarnesyltransferase, the counterpart of yeast DPR1/RAM1

Protein farnesyltransferase is a heterodimeric enzyme that attaches a farnesyl group to cysteine in ras proteins and other membrane-associated proteins. The β subunit contains the recognition site for the peptide substrates, but is inactive in the absence of the α subunit. A cloned cDNA for the rat β subunit predicts a protein of 437 amino acids whose mRNA is present in many tissues. Transfection of the β subunit cDNA produced farnesyltransferase activity in human kidney cells, but only when it was transfected together with a cDNA encoding part of the α subunit. Each of the subunits appeared to be unstable in the transfected cells unless the other subunit was present. The rat β subunit shows 37% sequence identity with the protein encoded by the yeast DPR1/RAM1 gene, indicating that DPR1/RAM1 is the yeast counterpart of the peptide-binding subunit of the mammalian farnesyltransferase.