Lorenz M C, Heitman J
Department of Genetics, Duke University Medical Center, Durham, NC 27710, USA.
EMBO J. 1997 Dec 1;16(23):7008-18. doi: 10.1093/emboj/16.23.7008.
Pseudohyphal differentiation, a filamentous growth form of the budding yeast Saccharomyces cerevisiae, is induced by nitrogen starvation. The mechanisms by which nitrogen limitation regulates this process are currently unknown. We have found that GPA2, one of the two heterotrimeric G protein alpha subunit homologs in yeast, regulates pseudohyphal differentiation. Deltagpa2/Deltagpa2 mutant strains have a defect in pseudohyphal growth. In contrast, a constitutively active allele of GPA2 stimulates filamentation, even on nitrogen-rich media. Moreover, a dominant negative GPA2 allele inhibits filamentation of wild-type strains. Several findings, including epistasis analysis and reporter gene studies, indicate that GPA2 does not regulate the MAP kinase cascade known to regulate filamentous growth. Previous studies have implicated GPA2 in the control of intracellular cAMP levels; we find that expression of the dominant RAS2(Gly19Val) mutant or exogenous cAMP suppresses the Deltagpa2 pseudohyphal defect. cAMP also stimulates filamentation in strains lacking the cAMP phosphodiesterase PDE2, even in the absence of nitrogen starvation. Our findings suggest that GPA2 is an element of the nitrogen sensing machinery that regulates pseudohyphal differentiation by modulating cAMP levels.
假菌丝分化是出芽酵母酿酒酵母的一种丝状生长形式，由氮饥饿诱导。目前尚不清楚氮限制调节这一过程的机制。我们发现，酵母中两个异源三聚体G蛋白α亚基同源物之一的GPA2调节假菌丝分化。Deltagpa2/Deltagpa2突变株在假菌丝生长方面存在缺陷。相反，GPA2的组成型活性等位基因即使在富含氮的培养基上也能刺激丝状化。此外，显性负性GPA2等位基因抑制野生型菌株的丝状化。包括上位性分析和报告基因研究在内的多项研究结果表明，GPA2并不调节已知调节丝状生长的MAP激酶级联反应。先前的研究表明GPA2参与细胞内cAMP水平的控制；我们发现显性RAS2(Gly19Val)突变体的表达或外源性cAMP可抑制Deltagpa2假菌丝缺陷。即使在没有氮饥饿的情况下，cAMP也能刺激缺乏cAMP磷酸二酯酶PDE2的菌株的丝状化。我们的研究结果表明，GPA2是氮感应机制的一个元件，通过调节cAMP水平来调节假菌丝分化。
