Feedback regulation of Ras2 guanine nucleotide exchange factor (Ras2-GEF) activity of Cdc25p by Cdc25p phosphorylation in the yeast Saccharomyces cerevisiae

The SDC25 gene of Saccharomyces cerevisiae is homologous to CDC25. Its 3' domain encodes a guanine nucleotide exchange factor (GEF) for Ras. Nevertheless, the GEF encoded by CDC24 is determinant for the Ras/cAMP pathway activation in growth. We demonstrate that the SDC25 gene product is a functional GEF for Ras: the complete SDC25 gene functionally replaces CDC25 when overexpressed or when transcribed under CDC25 transcriptional control at the CDC25 locus. Chimeric proteins between Sdc25p and Cdc25p are also functional GEFs for Ras. We also show that the two genes are differentially regulated: SDC25 is not transcribed at a detectable level in growth conditions when glucose is the carbon source. It is transcribed at the end of growth when nutrients are depleted and in cells grown on nonfermentable carbon sources. In contrast, CDC25 accumulation is slightly reduced when glucose is replaced by a nonfermentable carbon source.

Download Full-text

Identification of Novel, Evolutionarily Conserved Cdc42p-interacting Proteins and of Redundant Pathways Linking Cdc24p and Cdc42p to Actin Polarization in Yeast

Molecular Biology of the Cell ◽

10.1091/mbc.11.2.773 ◽

2000 ◽

Vol 11 (2) ◽

pp. 773-793 ◽

Cited By ~ 66

Author(s):

Erfei Bi ◽

John B. Chiavetta ◽

Herman Chen ◽

Guang-Chao Chen ◽

Clarence S. M. Chan ◽

...

Keyword(s):

Actin Cytoskeleton ◽

Double Mutant ◽

Synthetic Lethality ◽

Guanine Nucleotide Exchange Factor ◽

Guanine Nucleotide ◽

Nucleotide Exchange ◽

Yeast Saccharomyces Cerevisiae ◽

Exchange Factor ◽

Guanine Nucleotide Exchange ◽

Nucleotide Exchange Factor

In the yeast Saccharomyces cerevisiae, Cdc24p functions at least in part as a guanine-nucleotide-exchange factor for the Rho-family GTPase Cdc42p. A genetic screen designed to identify possible additional targets of Cdc24p instead identified two previously known genes, MSB1 and CLA4, and one novel gene, designated MSB3, all of which appear to function in the Cdc24p–Cdc42p pathway. Nonetheless, genetic evidence suggests that Cdc24p may have a function that is distinct from its Cdc42p guanine-nucleotide-exchange factor activity; in particular, overexpression of CDC42 in combination withMSB1 or a truncated CLA4 in cells depleted for Cdc24p allowed polarization of the actin cytoskeleton and polarized cell growth, but not successful cell proliferation.MSB3 has a close homologue (designatedMSB4) and two more distant homologues (MDR1 and YPL249C) in S. cerevisiae and also has homologues inSchizosaccharomyces pombe, Drosophila(pollux), and humans (the oncogenetre17). Deletion of either MSB3 orMSB4 alone did not produce any obvious phenotype, and the msb3 msb4 double mutant was viable. However, the double mutant grew slowly and had a partial disorganization of the actin cytoskeleton, but not of the septins, in a fraction of cells that were larger and rounder than normal. Like Cdc42p, both Msb3p and Msb4p localized to the presumptive bud site, the bud tip, and the mother-bud neck, and this localization was Cdc42p dependent. Taken together, the data suggest that Msb3p and Msb4p may function redundantly downstream of Cdc42p, specifically in a pathway leading to actin organization. From previous work, the BNI1, GIC1, andGIC2 gene products also appear to be involved in linking Cdc42p to the actin cytoskeleton. Synthetic lethality and multicopy suppression analyses among these genes, MSB, andMSB4, suggest that the linkage is accomplished by two parallel pathways, one involving Msb3p, Msb4p, and Bni1p, and the other involving Gic1p and Gic2p. The former pathway appears to be more important in diploids and at low temperatures, whereas the latter pathway appears to be more important in haploids and at high temperatures.

Download Full-text

Saccharomyces cerevisiae CDC25 [1028-1589] is a guanine nucleotide exchange factor for mammalian ras proteins and is ongenic in HIH3T3 cells

Biology of the Cell ◽

10.1016/0248-4900(92)90288-c ◽

1992 ◽

Vol 76 (2) ◽

pp. 229-229

Author(s):

Marie-Christine Chevallier-Multon ◽

Fabien Schweighoffer ◽

Isabelle Barlat ◽

Nicole Baudouy ◽

Isabelle Fath ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Guanine Nucleotide Exchange Factor ◽

Guanine Nucleotide ◽

Nucleotide Exchange ◽

Ras Proteins ◽

Exchange Factor ◽

Guanine Nucleotide Exchange ◽

Nucleotide Exchange Factor

Download Full-text

Characterization of Synthetic-Lethal Mutants Reveals a Role for the Saccharomyces cerevisiae Guanine-Nucleotide Exchange Factor Cdc24p in Vacuole Function and Na+ Tolerance

Genetics ◽

10.1093/genetics/147.1.43 ◽

1997 ◽

Vol 147 (1) ◽

pp. 43-55 ◽

Cited By ~ 4

Author(s):

William H White ◽

Douglas I Johnson

Keyword(s):

Saccharomyces Cerevisiae ◽

Cell Polarity ◽

Synthetic Lethality ◽

Guanine Nucleotide Exchange Factor ◽

Guanine Nucleotide ◽

Nucleotide Exchange ◽

Synthetic Lethal ◽

Exchange Factor ◽

Guanine Nucleotide Exchange ◽

Nucleotide Exchange Factor

Abstract Cdc24p is the guanine-nucleotide exchange factor for the Cdc42p GTPase, which controls cell polarity in Saccharomyces cerevisiae. To identify new genes that may affect cell polarity, we characterized six UV-induced csl (CDC24 synthetic-lethal) mutants that exhibited synthetic-lethality with cdc24-4ts at 23°. Five mutants were not complemented by plasmid-borne CDC42, RSRI, BUD5, BEM1, BEM2, BEM3 or CLA4 genes, which are known to play a role in cell polarity. The csl3 mutant displayed phenotypes similar to those observed with calcium-sensitive, Pet− vma mutants defective in vacuole function. CSL5 was allelic to VMA5, the vacuolar H+-ATPase subunit C, and one third of cs15 cdc24-4ts cells were elongated or had misshapen buds. A cdc24-4ts Δvma5::LEU2 double mutant did not exhibit synthetic lethality, suggesting that the csl5/vma5 cdc24-4ts synthetic-lethality was not simply due to altered vacuole function. The cdc24-4ts mutant, like Δvma5::LEU2 and cs13 mutants, was sensitive to high levels of Ca2+ as well as Na+ in the growth media, which did not appear to be a result of a fragile cell wall because the phenotypes were not remedied by 1 m sorbitol. Our results indicated that Cdc24p was required in one V-ATPase mutant and another mutant affecting vacuole morphology, and also implicated Cdc24p in Na+ tolerance.

Download Full-text