Reversion of deformed ras1¯ cells of Schizosaccharomyces pombe to rod-like cells by nutrient stimulation

The reversion of the highly spherical rasl phenotype of the sterile mutant of Schizosaccharomyces pombe was examined by fluorescence microscopy of Calcofluor- and rhodamine phalloidin-labelled cells and by freeze-fracturing. Rapid and dramatic changes occurred in cell shape after a nutritional stimulus, with cells regaining their rod-like cell shape during successive cell divisions. This was achieved by restoration of the cell wall architecture and of the invaginated state of the plasma membrane. This is the first demonstration of a nutrient-induced reversion of rasl ~ S. pombe cells from rounded to rod-like cell shape.