MUTATIONAL ANALYSIS OF MORPHOLOGIC DIFFERENTIATION IN SACCHAROMYCES-CEREVISIAE

A genetic analysis was undertaken to investigate the mechanisms contro lling cellular morphogenesis in Saccharomyces cerevisiae. Sixty mutant strains exhibiting abnormally elongated cell morphology were isolated . The cell elongation phenotype in at least 26 of the strains resulted from a single recessive mutation. These mutations, designated generic ally elm (elongated morphology), defined 14 genes; two of these corres ponded to the previously described genes GRRI and CDC12. Genetic inter actions between mutant alleles suggest that several ELM genes play rol es in the same physiological process. The cell and colony morphology a nd growth properties of many elm mutant strains are similar to those o f wild-type yeast strains after differentiation in response to nitroge n limitation into the pseudohyphal form. Each elm mutation resulted in multiple characteristics of pseudohyphal cells, including elongated c ell shape, delay in cell separation, simultaneous budding of mother an d daughter cells, a unipolar budding pattern, and/or the ability to gr ow invasively beneath the agar surface. Mutations in 11 of the 14 ELM gene loci potentiated pseudohyphal differentiation in nitrogen-limited medium. Thus, a subset of the ELM genes are likely to affect control or execution of a defined morphologic differentiation pathway in S. ce revisiae.