Structural homology among mammalian and Saccharomyces cerevisiae isoprenyl-protein transferases.
Farnesyl-protein transferase (FTase) purified from rat or bovine brain is an alpha/beta heterodimer, comprised of subunits having relative molecular masses of approximately 47 (alpha) and 45 kDa (beta). In the yeast Saccharomyces cerevisiae, two unlinked genes, RAM1/DPR1 (RAM1) and RAM2, are required for FTase activity. To explore the relationship between the mammalian and yeast enzymes, we initiated cloning and immunological analyses. cDNA clones encoding the 329-amino acid COOH-terminal domain of bovine FTase alpha-subunit were isolated. Comparison of the amino acid sequences deduced from the alpha-subunit cDNA and the RAM2 gene revealed 30% identity and 58% similarity, suggesting that the RAM2 gene product encodes a subunit for the yeast FTase analogous to the bovine FTase alpha-subunit. Antisera raised against the RAM1 gene product reacted specifically with the beta-subunit of bovine FTase, suggesting that the RAM1 gene product is analogous to the bovine FTase beta-subunit. Whereas a ram1 mutation specifically inhibits FTase, mutations in the CDC43 and BET2 genes, both of which are homologous to RAM1, specifically inhibit geranylgeranyl-protein transferase (GGTase) type I and GGTase-II, respectively. In contrast, a ram2 mutation impairs both FTase and GGTase-I, but has little effect on GGTase-II. Antisera that specifically recognized the bovine FTase alpha-subunit precipitated both bovine FTase and GGTase-I activity, but not GGTase-II activity. Together, these results indicate that for both yeast and mammalian cells, FTase, GGTase-I, and GGTase-II are comprised of different but homologous beta-subunits and that the alpha-subunits of FTase and GGTase-I share common features not shared by GGTase-II.
Kohl
N E
NE
Department of Cancer Research, Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania 19486.
Diehl
R E
RE
Schaber
M D
MD
Rands
E
E
Soderman
D D
DD
He
B
B
Moores
S L
SL
Pompliano
D L
DL
Ferro-Novick
S
S
Powers
S
S
D019883:Alkyl and Aryl Transferases; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D003001:Cloning, Molecular; D004247:DNA; D015151:Immunoblotting; D008322:Mammals; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D016415:Sequence Alignment; D014166:Transferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D004247:DNA; D014166:Transferases; D019883:Alkyl and Aryl Transferases; C064911:p21(ras) farnesyl-protein transferase