BTS1 ENCODES A GERANYLGERANYL DIPHOSPHATE SYNTHASE IN SACCHAROMYCES-CEREVISIAE

Protein prenylation utilizes different types of isoprenoids groups, na mely farnesyl and geranylgeranyl, to modify proteins. These lipophilic moieties attach to carboxyl-terminal cysteine residues to promote the association of soluble proteins to membranes. Most prenylated protein s are geranylgeranylated. Geranylgeranylation is catalyzed by two diff erent prenyltransferases, the type I and type II geranylgeranyl transf erases, both of which utilize geranylgeranyl diphosphate as a lipid do nor. In the yeast Saccharomyces cerevisiae, the BET2 gene encodes the beta-subunit of the type II geranylgeranyl transferase. Mutations in t his gene cause a defect in the geranylgeranylation of small GTP-bindin g proteins that mediate vesicular traffic. In an attempt to analyze th ose genes whose products may interact with Bet2, we isolated a suppres sor of the bet2-1 mutant. This suppressor gene, called BTS1, encodes t he yeast geranylgeranyl diphosphate synthase. BTS1 is not essential fo r the vegetative growth of cells; however, disrupting it impedes the g eranylgeranylation of many cellular proteins and renders cells cold se nsitive for growth. Our findings imply that BTS1 suppresses the bet2-1 mutant by increasing the intracellular pool of geranylgeranyl diphosp hate.