ALPHA FACTOR SIGNALING PEPTIDE – Hormones

The life cycle of Saccharomyces cerevisiae,also known as the brewer’s and the baker’s yeast,is characterized by both haploid and diploid phases. Indeed,yeasts are organized in two haploid types,known as a and α cells (MATa and MATα),that can either proliferate individually,using mitosis,or fuse together to form MATa/MATα diploids. For two haploid cells to mate,mating factors are needed. These pheromones induce G-Protein Coupled Receptor‘s (GPCR) conformational changes,which allow G-protein migration in the plasma membrane. GPCRs are present on both a and α yeast cells and turn into Guanine nucleotide Exchange Factors (GEF) upon G-protein release. The receptor’s « new activity » leads to guanosine diphosphate (GDP) exchange by guanosine triphosphate (GTP) on the G-protein,which will recruit STE 5 to allow Fus3 protein phosphorylation. Phosphate addition on Fus3 enables its fusion to the cell’s plasma membrane in order to activate formin proteins by phosphorylation. Formin proteins being involved in the polymerization of microfilaments,their consequent growth within the cell will form shmoo projections to enable complete mating of MATa and MATα cells,towards MATa/MATα diploid cell that can undergo mitosis and meiosis to create new haploid spores. To induce a yeast cells’ shmoo projection,WHWLQLKPGQPMY pheromone (or alpha mating factor) is produced by α yeast cells. This signaling peptide is part of the MFAL1_YEAST protein (UniProt: P01149) that excretes its active factor into the culture medium to act on the opposite mating type). α mating factor is a 13 residues peptide inducing the expression of necessary mating genes ( 200 genes – 3% of the yeast’s genome) to arrest yeast cell cycle in the G1 phase,while altering cell surface and nuclear determinants,towards MATa and MATα fusion. WHWLQLKPGQPMY interacts with its complementary pheromone,a-factor,which is a 12 residues peptide (YIIKGVFWDPAC) that is covalently attached to farnesyl to generate the appropriate response upon α pheromone activation. IC-PEPTIDE offers α mating factor WHWLQLKPGQPMY to study: Cell cycle Cellular morphology Transcriptional induction Signal transduction pathways

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