In the yeast Saccharomyccs cerevwise, qiutations in either of two unlinked genes, RAM)-1or RAM2, abolish the farnesyltrnsferae activity responsible for prenylation of Ras proteins and the a-factor mating pheromone. Here we report that thefunction of RAM) antd RAM2 genme is required for the membrane laliation ofRas proteins and a-factor. The RAM2 gene was sequenced and can encode a 38-kDa protein.We examined tie functional interaction ofRAM2 andRAMf by expressing the genes in Escherchia colt. Extracts derived from an E. coil strain that coexpressed RAM] and RAM2 efficiently farnesylated a-factor peptide and Ras protein substrates. In contrast, extracts derived from E. colN strains that expressed either RAM gene alone were devoid of activity; however, when the latter extracts were mixed, protein farnesyltransferaSe activity was reconstituted. These results indicate that the yeast farnesyl-protein transferase is comprised of Raml and Ram2 polypeptides. Although Raml is a component of the enzyme, disruption of the RAM) gene in yeast was not lethal indicating that the Raml-Ram2 farnesyltserase is not essential for viability. In contrast, disruption of RAM2 was lethal, suggesting that Ram2 has an essential function in addition to its role with Raml in protein farnesylation.The post-translational modification of proteins by the covalent attachment of isoprenoid groups plays an important role in the membrane targeting of various proteins (1-5). Three classes of prenylated proteins in eukaryotic cells have been described. The first class, represented by certain fungal mating pheromones, Ras proteins, and nuclear lamins, is initially synthesized with a C-terminal CAAX sequence, where X = Ser, Cys, Met, or Ala, and is modified by thioether linkage of a C15 farnesyl group to the cysteine residue (6-9). The second class of prenylated proteins, represented by the y subunits of certain heterotrimeric G proteins and various Ras-like proteins, is initially synthesized with different C-terminal CAAX sequences, in which X = Leu or Phe, and is modified by the attachment of a C20 geranylgeranyl group to the cysteine residue (10-12). Members of both of these classes of prenylated proteins are subsequently processed by proteolytic removal of the three terminal amino acids and methylation of the newly exposed carboxyl group of the prenyl-cysteine (6, 10-15). The third class of prenylated proteins, represented by the Yptl/Sec4 (Rab) family of Ras-like GTPases that terminate with the sequence CC or CXC, is also geranylgeranylated at a C-terminal cysteine residue(s) (16)(17)(18).

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Early exposure to some mild stresses can slow down the aging process and extend lifespan, raising the question of how early life stress might impact the somatic health of aged animals. Here, we reveal that early life heat experience triggers the establishment of epigenetic memory in soma, which promotes long-lasting stress responses and longevity in C . elegans . Unlike lethal heat shock, mild heat activates a unique transcriptional program mimicking pathogen defense responses, characterized by the enhanced expression of innate immune and detoxification genes. Surprisingly, the expression of defense response genes persists long after heat exposure, conferring enhanced stress resistance even in aged animals. Further studies identify the histone acetyltransferase CBP-1 and the chromatin remodeling SWI/SNF complex as epigenetic modulators of the long-lasting defense responses. Histone acetylation is elevated by heat stress and maintained into agedness thereafter. Accordingly, histone acetylation levels were increased on the promoters of defense genes. Moreover, disruption of epigenetic memory abrogates the longevity response to early hormetic heat stress, indicating that long-lasting defense responses are crucial for the survival of aged animals. Together, our findings provide mechanistic insights into how temperature stress experienced in early life provides animals with lifetime health benefits.

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