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  • Title: Structural homology among mammalian and Saccharomyces cerevisiae isoprenyl-protein transferases.
    Author: Kohl NE, Diehl RE, Schaber MD, Rands E, Soderman DD, He B, Moores SL, Pompliano DL, Ferro-Novick S, Powers S.
    Journal: J Biol Chem; 1991 Oct 05; 266(28):18884-8. PubMed ID: 1918005.
    Abstract:
    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.
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