CDNA CLONING AND EXPRESSION OF RAT AND HUMAN PROTEIN GERANYLGERANYLTRANSFERASE TYPE-I

Protein geranylgeranyltransferase type-I (GGTase-I) transfers a gerany lgeranyl group to the cysteine residue of candidate proteins containin g a carboxyl-terminal CAAX (C, cysteine; A, aliphatic amino acid; X, a ny amino acid) motif in which the ''X'' residue is leucine. The enzyme is composed of a 48-kilodalton alpha subunit and a 43-kilodalton beta subunit. Peptides isolated from the alpha subunit of GGTase-I were sh own to be identical with the alpha subunit of a related enzyme, protei n farnesyltransferase. Overlapping cDNA clones containing the complete coding sequence for the beta subunit of GGTase-I were obtained from r at and human cDNA libraries. The cDNA clones from both species each pr edicted a protein of 377 amino acids with molecular masses of 42.4 kil odaltons (human) and 42.5 kilodaltons (rat). Amino acid sequence compa rison suggests that the protein encoded by the Saccharomyces cerevisia e gene CDC43 is the yeast counterpart of the mammalian GGTase-I beta s ubunit. Co-expression of the GGTase-I beta subunit cDNA together with the alpha subunit of protein farnesyltransferase in Escherichia coli p roduced recombinant GGTase-I with electrophoretic and enzymatic proper ties indistinguishable from native GGTase-I.