Isolation of a second yeast Saccharomyces cerevisiae gene (GPA2) coding for guanine nucleotide-binding regulatory protein: studies on its structure and possible functions.

Abstract

In a previous paper, we demonstrated that a gene coding for a protein homologous to the alpha subunit of mammalian guanine nucleotide-binding regulatory (G) proteins occurs in Saccharomyces cerevisiae. The gene, designated GPA1, encodes a protein (GP1 alpha) of 472 amino acids with a calculated Mr of 54,075. Here we report the isolation of another G-protein-homologous gene, GPA2, which encodes an amino acid sequence of 449 amino acid residues with a Mr of 50,516. The predicted primary structure of the GPA2-encoded protein (GP2 alpha) is homologous to mammalian G proteins [inhibitory and stimulatory G proteins (Gi and Gs, respectively), a G protein of unknown function (Go), and transducins (Gt)] as well as yeast GP1 alpha. When aligned with the alpha subunit of Gi (Gi alpha) to obtain maximal homology, GP2 alpha was found to contain a stretch of 83 additional amino acid residues near the NH2 terminus. The gene was mapped in chromosome V, close to the centromere. Haploid cells carrying a disrupted GPA2 gene are viable. Cells carrying a high copy number of plasmid GPA2 (YEpGPA2) had markedly elevated levels of cAMP and could suppress a temperature-sensitive mutation of RAS2. These results suggest that GPA2 may be involved in the regulation of cAMP levels in S. cerevisiae.

Life in the midst of scarcity: adaptations to nutrient availability in Saccharomyces cerevisiae

“…Gpr1 belongs to the G protein-coupled seven-transmembrane receptor (GPCR) superfamily (Yun et al 1997;Xue et al 1998) and Gpa2 is a member of the heterotrimeric G protein a subunit (G a ) protein family (Nakafuku et al 1988). Addition of glucose to derepressed cells activates Gpr1, which in turn stimulates the exchange of GDP for GTP on Gpa2 (Kraakman et al 1999a).…”

“…This probably ensures that the cAMP-PKA pathway is only fully activated when glucose levels are high enough to switch easily from respiration to fermentation. GTP-bound Gpa2 activates the cAMP-PKA pathway and this is most probably through stimulation of adenylate cyclase (Nakafuku et al 1988;Kubler et al 1997;Lorenz and Heitman 1997;Colombo et al 1998;Rolland et al 2000;Peeters et al 2006). Gpa2 interacts with Rgs2, a member of the family of regulators of G protein signalling (RGS), that negatively regulates the Gpa2-GTP signal by stimulating the intrinsic GTPase activity of Gpa2 (Versele et al 1999).…”

Sequence elements that contribute to the degradation of yeast Gα

“…A second yeast G␣ protein, Gpa2, is 45% identical and 60% homologous to Gpa1 but is not required for mating (Nakafuku et al 1988). It has been reported recently that Gpa2 modulates growth and pseudohyphal development by regulating intracellular cAMP levels (Kubler et al 1997;Lorenz & Heitman 1997).…”

The glucose‐induced polyphosphoinositides turnover in Saccharomyces cerevisiae is not dependent on the CDC25‐RAS mediated signal transduction pathway

“…The overexpression of CDC25 product does not markedly stimulate the PI turnover as well as it does not change significatively the intracellular cAMP level ( [12], Frascotti et al, manuscript in preparation). Since Gproteins, different from RAS proteins, are present in yeast [16,17], it can be tentatively suggested that another G-protein may be responsible for the PI turnover in yeast, while RAS1 and RAS2 proteins work normally only on the adenylate cyclase pathway. An 'activating' RAS mutation, like RAS2 vaIl9 which may alter the target specificity of the protein, could originate the observed hyperstimulatory effect.…”