A specific mutation in Saccharomyces cerevisiae adenylate cyclase, Cyrl(K1876M), eliminates glucose- and acidification-induced cAMP signalling and delays glucose-induced loss of stress resistance

The cAMP-protein kinase A (PKA) pathway in the yeast Saccharomyces cerevisi ae plays a major role in the control of metabolism. proliferation and stres s resistance. Derepressed cells show a rapid increase in the cAMP level (wi thin 1 min) after addition of glucose or after intracellular acidification. A specific mutation in adenylate cyclase, the enzyme that catalyzes the sy nthesis in cAMP, largely prevents both cAMP responses. The responsible muta tion was originally called lcr1 (for lack of (c) under bar AMP (r) under ba r esponses); lcr1 was later identified as allelic with CYR1/CD35. The mutat ion was introduced into the CYR1 gene of a W303-1A wild type strain, which resulted in a large decrease in cAMP signalling. Furthermore, there was a s trong reduction in GTP/Mg2+-stimulated but not in Mn2+-stimulated adenylate cyclase activity in isolated plasma membranes, which is consistent with th e absence of signalling through adenylate cyclase in vivo. Glucose-induced activation of trehalase was reduced and mobilization of trehalose and glyco gen and loss of stress resistance were delayed in the lcr1 mutant. Because of the absence of cAMP signalling during exponential growth on glucose, it was concluded that glucose-induced cAMP signalling is restricted to the tra nsition from gluconeogenic/respiratory to fermentative growth. Activation o f the PKA pathway is mediated by a G protein (either Ras1/Ras2 or Gpa2). Co nstitutive activation of the pathway by Ras(val19) or Gpa(val132) has a neg ative effect on glycogen and trehalose accumulation and heat shock survival . The lcr1 mutation partially suppresses this effect indicating that the ta rget sites of the two G-proteins on adenylate cyclase might have at least a part in common. (C) 2000 Elsevier Science B.V. All rights reserved.