New roles for CDC25 in growth control, galactose regulation and cellular differentiation in Saccharomyces cerevisiae

Abstract

Living organisms display large differences in stress resistance throughout their life cycles. To study the coordinated regulation of development and stress responses in exponentially growing yeast, mutants that displayed elevated heat-shock resistance at this stage were screened for. Here, two new mutant alleles ofCDC25inSaccharomyces cerevisiae,cdc25-21andcdc25-22, are described. During exponential growth in glucose at 25 °C, these mutants are resistant to heat, oxidative, osmotic and ionic shock, accumulate stress-protein transcripts, show slow growth rates, thick cell walls and glycogen hyperaccumulation and lack cAMP signalling in response to glucose. Genetic and cellular analyses revealed that the stationary-phase phenotypes ofcdc25-21andcdc25-22mutants are not due to entrance to a G0state during exponential growth, but are the result of a prolonged G1phase. It was found that, in the W303 background,CDC25is dispensable for growth in glucose media. However,CDC25is essential for growth in galactose, in non-fermentable carbon sources and under continuous incubation at 38 °C. In conclusion, the function of the catalytic, C-terminal domain of Cdc25p is not only important for fermentative growth, but also for growth in non-fermentable carbon sources and to trigger galactose derepression.