Farnesylated a-factor is a post-translationally modified mating pheromone derived from Saccharomyces cerevisiae. The addition of a farnesyl group to the C-terminus is crucial for the biological activity of the a-factor.

During the mating of Saccharomyces cerevisiae, the haploid state of yeast can be either α-type or a-type. Mating pheromones produced by these haploid cells can induce two different cell types to mate. The α-factor is released from α-type cells and bind to the G-protein coupled receptor (GPCR) Ste2p on a-cells, whereas the a-factor is released from a-type cells and binds to the GPCR Ste3p on α-cells.