REVERSION OF DEFORMED RAS1- CELLS OF SCHIZOSACCHAROMYCES-POMBE TO ROD-LIKE CELLS BY NUTRIENT STIMULATION

The reversion of the highly spherical ras1- phenotype of the sterile m utant of Schizosaccharomyces pombe was examined by fluorescence micros copy of Calcofluor- and rhodamine phalloidin-labelled cells and by fre eze-fracturing. Rapid and dramatic changes occurred in cell shape afte r a nutritional stimulus, with cells regaining their rod-like cell sha pe during successive cell divisions. This was achieved by restoration of the cell wall architecture and of the invaginated state of the plas ma membrane. This is the first demonstration of a nutrient-induced rev ersion of ras1- S. pombe cells from rounded to rod-like cell shape.