Figure 1. Sexual communication via pheromones and their corresponding receptors.

A) The mating system of S. cerevisiae. The two haploid S. cerevisiae cell types, a (white) and α (dark gray) express seven-transmembrane, G-protein coupled receptors that detect the presence of small peptides secreted by the opposite mating type. MATa cells secrete a-factor (red a) and express the α-factor receptor (Ste2, blue semi-circular receptor) at their surface; MATα cells secrete α-factor (blue α) and express the a-factor receptor Ste3 (red, U-shaped receptor) at their surface,. When the two cells find each other, they can fuse to form a diploid (light gray) cell that can divide mitotically. B) Pheromone asymmetry between the Ascomycetes and the Basidiomycetes: the Ascomycetes, which include Saccharomyces cerevisiae and Sordaria macrospora, communicate via two different types of pheromones, unmodified, α-factor like peptides and lipid-modified, a-factor-like peptides. The Basidiomycetes, like Schizophyllum commune, only use lipid-modified a-factor-like pheromones. The letter a represents lipid-modified pheromones and the letter α represents α-factor-like peptides. Letters are reversed for pheromones derived from species other than S. cerevisiae. The sequences for the α-factor like peptides from S. cerevisiae and S. macrospora are shown in blue and green, respectively. The sequences for the a-factor like pheromones for S. cerevisiae and S. commune are shown in red and yellow, respectively. This color code is common to all figures. C) Examples of artificial mating types. In S. cerevisiae, two cells, expressing different mating loci (MATa or MATα) communicate using asymmetric pheromones (a- and α-factor-like peptides) and their corresponding receptors (top line). We disrupted these asymmetries by generating artificial mating types that communicate via two different α-factor-like (middle line) or two different a-factor-like peptides, and also produced cells that expressed complementary pairs of receptors and pheromones but expressed the same mating type locus (bottom line). Legend: Red: a-factor (aF_cer) and a-factor (aR_cer) receptor from S. cerevisiae. Blue: α-factor (αF_cer) and α-factor receptor (αR_cer) from S. cerevisiae. Green: α-factor (αF_mac) and α-factor receptor (αR_mac) from S. macrospora. Yellow: a-factor (aF_com) and a-factor receptor (aR_com) from S. commune.