The order Schizosaccharomycetales contains a dimorphic and two yeast species. Sch. japonicus can form both yeast cells and mycelium, depending on the substrate and the culturing conditions. Sch. pombe is a strictly unicellular organism, but it can be forced to form mycelial cell chains by inactivating members of the sep gene family. The mutations in most of the sep genes confer pleitropic phenotypes indicating functional involvement in MAP-kinase-mediated signalling pathways. Two of them were found to encode transcription factor homologues of other eukaryotes.