Disease relevance of STE14

• We demonstrate here that STE14 is the structural gene for this enzyme by expression of its product as a fusion protein in Escherichia coli, an organism in which this activity is lacking [1].
• A Leptospira interrogans enzyme with similarity to yeast Ste14p that methylates the 1-phosphate group of lipid A [2].

High impact information on STE14

• The Saccharomyces cerevisiae STE14 gene encodes a methyltransferase that mediates C-terminal methylation of a-factor and RAS proteins [1].
• It is notable that cells lacking STE14 methyltransferase activity exhibit no detectable impairment of RAS function or cell viability [1].
• We also show that a-factor, RAS1 and RAS2 are physiological methyl-accepting substrates for this enzyme by demonstrating that these proteins are not methylated in a ste14 null mutant [1].
• Mapping data indicate that STE14 resides on chromosome IV, tightly linked to ADE8 [3].
• By analysis of ste14 null alleles, we demonstrated that MATa ste14 mutants are unable to mate but are viable and exhibit no apparent growth defects [3].

Biological context of STE14

• Nucleotide sequence of the yeast STE14 gene, which encodes farnesylcysteine carboxyl methyltransferase, and demonstration of its essential role in a-factor export [3].
• Additional analysis of ste14 ras 1 and ste14 ras2 double mutants, which grow normally, reinforces our previous conclusion that RAS function is not significantly influenced by its methylation status [3].
• To show that the loss of methyltransferase activity is a direct result of the ste14 mutation, we transformed ste14 mutant cells with a plasmid complementing the mating defect of this strain and found that active enzyme was produced [4].
• We examine a-factor biogenesis in a ste14 null mutant by metabolic labeling and immunoprecipitation and demonstrate that although proteolytic processing and membrane localization of a-factor are normal, the ste14 null mutant exhibits a profound block in a-factor export [3].
• The isoprenoid substrate specificity of isoprenylcysteine carboxylmethyltransferase: development of novel inhibitors [5].

Anatomical context of STE14

• This study focuses on the isoprenylcysteine carboxylmethyltransferase (Icmt) enzyme from Saccharomyces cerevisiae, Ste14p, the founding member of a homologous family of endoplasmic reticulum membrane proteins present in all eukaryotes [6].
• According to this model most of the Ste14p hydrophilic regions are located in the cytosol [7].
• Because the physiological substrates of Ste14p, such as Ras and the yeast a-factor precursor, are isoprenylated and reside on the cytosolic side of membranes, the Ste14p residues involved in enzymatic activity are predicted to be cytosolically disposed [7].

Associations of STE14 with chemical compounds

• Farnesyl cysteine C-terminal methyltransferase activity is dependent upon the STE14 gene product in Saccharomyces cerevisiae [4].
• When cells were incubated in the presence of the protein synthesis inhibitor cycloheximide, little or no methylation of the STE14-dependent species was detected while the methylation of the STE14-independent substrates was unaffected [8].
• These isoprenoid-modified analogs of the minimal Icmt substrate N-acetyl-S-farnesyl-L-cysteine (AFC) were synthesized from newly and previously prepared farnesol analogs [5].
• In this study, we developed a variety of substrates and inhibitors of Icmt that vary in the isoprene moiety in order to gain information about the nature of the lipophilic substrate binding site [5].
• Saccharomyces cerevisiae ste14 mutants that lack RAS and a-factor carboxyl methyltransferase activity are also unable to methylate farnesyl and geranylgeranylcysteine derivatives [9].

Other interactions of STE14

• In yeast, the farnesyltransferase (FTase) is encoded by the RAM1(DPR1) and RAM2 genes, and the methyltransferase is the product of STE14 [10].
• However, addition of yeast extracts from wild type, ram1, or ste14 mutants resulted in the removal of the -aaX residues from prenylated CaaX box peptides [10].
• This set of genes includes those, termed a-specific STE genes (STE2, STE6, and STE14), which are required for mating by a cells but not by alpha cells [11].
• In addition to catalyzing methylation of AFC, we also show that purified Ste14p methylates a known in vivo substrate, Ras2p [6].

Analytical, diagnostic and therapeutic context of STE14

• Base treatment converted the normal pheromone into a form which was biologically inactive and which comigrated with the ste14 form of the peptide upon thin-layer chromatography [12].
• We demonstrate by immunofluorescence and subcellular fractionation that Ste14p and its associated activity are localized to the endoplasmic reticulum (ER) membrane of yeast [13].
• We have also generated ste14 mutants by random and site-directed mutagenesis to identify residues of Ste14p that are important for activity [7].

References