Amino acid sequences of a-factor mating peptides from Saccharomyces cerevisiae

The molecular structure of a-factor, the mating hormone produced by mating type a cells of Saccharomyces cerevisiae, has been investigated. In culture filtrates of a cells four oligopeptides (a1 to a4) exhibiting a-factor activity have been found. These peptides have been isolated and their amino acid sequences have been determined. The a-factor peptides comprise two (apparently identical) pairs, a1/a2 and a3/a4, which differ in an interchange at position 6 of a valine in a1/a2 for a leucine in a3/a4. a1 and a4, which can be obtained by oxidation with H2O2 of purified a2 and a3, respectively, obviously represent oxidation artifacts formed under the conditions of culture. The amino acid sequences determined for the a-factor peptides are Tyr-Ile-Ile-Lys-Gly-Val Leu-Phe-Trp-Asp-Pro-Ala-Cys. Several lines of evidence suggest that the carboxyl-terminal cysteine residue is S-alkylated by a hydrophobic moiety.