Ras1 and Ras2 play antagonistic roles in regulating cellular cAMP level, stationary-phase entry and stress response in Candida albicans.
The GTPase Ras1 activates the yeast-to-hypha transition in Candida albicans by activating cAMP synthesis. Here, we have characterized Ras2. Ras2 belongs to a group of atypical Ras proteins in some fungal species that share poor identity with other Ras GTPases with many variations in conserved motifs thought to be crucial for Ras-associated activities. We find that recombinant Ras2 is enzymatically as active as Ras1. However, only RAS1 can rescue the lethality of the Saccharomyces cerevisiae ras1 ras2 mutant, suggesting functional divergence of the two genes. ras2Delta is normal in hyphal growth, but deleting RAS2 in the ras1Delta background greatly aggravates the hyphal defect, indicating that Ras2 also has a role in hyphal development. Strikingly, while RAS1 deletion causes a approximately 20-fold decrease in cellular cAMP, further deletion of RAS2 restores it to approximately 30% of the wild-type level. Consistently, while the ras1Delta mutant enters the stationary phase prematurely, the double mutant does so normally. Moreover, ras1Delta cells exhibit increased resistance to H(2)O(2) and higher sensitivity to the heavy metal Co(2+), whereas ras2Delta cells show the opposite phenotypes. Together, our data reveal a novel regulatory mechanism by which two antagonizing Ras GTPases balance each other in regulating multiple cellular processes in C. albicans.
Zhu
Yong
Y
Institute of Molecular and Cell Biology, A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Singapore 138673, Singapore.
Fang
Hao-Ming
HM
Wang
Yan-Ming
YM
Zeng
Gui-Sheng
GS
Zheng
Xin-De
XD
Wang
Yue
Y
D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000633:toxicity; D002176:Candida albicans / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D003035:Cobalt / Q000633:toxicity; D000242:Cyclic AMP / Q000378:metabolism*; D005656:Fungal Proteins / Q000502:physiology*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005816:Genetic Complementation Test; D006861:Hydrogen Peroxide / Q000633:toxicity; D025301:Hyphae / Q000254:growth & development; D050296:Microbial Viability; D008969:Molecular Sequence Data; D010802:Phylogeny; D016415:Sequence Alignment; D013312:Stress, Physiological
D000935:Antifungal Agents; D005656:Fungal Proteins; D003035:Cobalt; D006861:Hydrogen Peroxide; D000242:Cyclic AMP; D020558:GTP Phosphohydrolases