Pheromone-induced transcription in S. pombe. A. Diagram of pheromone communication. Prior to mating, M cells and P cells secrete the two pheromones, P-factor (squares) and M-factor (circles) that can bind to specific receptors present on the surface of the opposite cell type. This causes activation of an intracellular signalling pathway that prepares the cells for mating. Following successful conjugation, continued pheromone stimulation allows entry into meiosis and sporulation. B. Types of pheromone regulated transcription. Bar diagrams symbolizing the transcription levels in cells growing in the presence of nitrogen (+), starved for nitrogen (-) or starved for nitrogen in the presence of M-factor (-/M) or P-factor (-/P). The left panel illustrates the expression pattern in P cells, while the right panel shows the pattern in M cells. The following types of genes are depicted: (1) a gene that is induced by nitrogen starvation and further boosted by pheromone signalling, (2) a gene that has an absolute requirement for both nitrogen starvation and pheromone signalling, (3) an M-specific gene, (4) a P-specific gene.