Division-site selection, cell separation, and formation of anucleate minicells inSchizosaccharomyces pombe mutants resistant to cell-wall lytic enzymes

Summary In most eukaryotic organisms that have cell walls, cell separation or cytokinesis is a degradative enzymatic process. In the fission yeastSchizosaccharomyces pombe, it is a post-M-phase event that includes the degradation of part of the cell wall and the primary septum. We describe the isolation of mutants partially defective in cytokinesis by enrichment of clones resistant to cell-wall lytic enzymes. The mutations confer mycelial morphology (chains of non-separated cells) and define four genes.Sep2-SA2 was subjected to detailed genetic and cytological analysis. Its cells frequently form complex septa composed of multiple layers, which appear as twin septa separated by anucleate minicells if the cell length is extended. This suggests that a polar signal-like mechanism may also operate inS. pombe during division-site selection andsep2⁺ takes part in it.Sep2⁺ seems to be involved in several cell cycle functions because its mutation can transiently block cell-cycle progression after nuclear division and provoke a transition from haploidy to diploidy in the double mutantsep2-SA2 cexl-SA2. Cexl-SA2 is another novel mutation which causes cell-length extension.Abbreviations DAPI 4,6-diamidino-2-phenylindole - YEA yeast extract agar - YEL yeast extract liquid - SMA synthetic minimal agar - MEA malt extract agar