Glucose monitoring in fission yeast via the Gpa2 galpha, the git5 Gbeta and the git3 putative glucose receptor.
The fission yeast Schizosaccharomyces pombe responds to environmental glucose by activating adenylate cyclase. The resulting cAMP signal activates protein kinase A (PKA). PKA inhibits glucose starvation-induced processes, such as conjugation and meiosis, and the transcription of the fbp1 gene that encodes the gluconeogenic enzyme fructose-1,6-bisphosphatase. We previously identified a collection of git genes required for glucose repression of fbp1 transcription, including pka1/git6, encoding the PKA catalytic subunit, git2/cyr1, encoding adenylate cyclase, and six "upstream" genes required for adenylate cyclase activation. The git8 gene, identical to gpa2, encodes the alpha subunit of a heterotrimeric guanine-nucleotide binding protein (Galpha) while git5 encodes a Gbeta subunit. Multicopy suppression studies with gpa2(+) previously indicated that S. pombe adenylate cyclase activation may resemble that of the mammalian type II enzyme with sequential activation by Galpha followed by Gbetagamma. We show here that an activated allele of gpa2 (gpa2(R176H), carrying a mutation in the coding region for the GTPase domain) fully suppresses mutations in git3 and git5, leading to a refinement in our model. We describe the cloning of git3 and show that it encodes a putative seven-transmembrane G protein-coupled receptor. A git3 deletion confers the same phenotypes as deletions of other components of the PKA pathway, including a germination delay, constitutive fbp1 transcription, and starvation-independent conjugation. Since the git3 deletion is fully suppressed by the gpa2(R176H) allele with respect to fbp1 transcription, git3 appears to encode a G protein-coupled glucose receptor responsible for adenylate cyclase activation in S. pombe.
Welton
R M
RM
Department of Biology, Boston College, Chestnut Hill, Massachusetts 02467, USA.
Hoffman
C S
CS
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D006597:Fructose-Bisphosphatase; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C416142:git3 protein, S pombe; C101525:git5 protein, S pombe; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; C111172:FBP1 protein, S cerevisiae; D006597:Fructose-Bisphosphatase; D020962:Heterotrimeric GTP-Binding Proteins; C540695:gpa2 protein, S pombe; D000262:Adenylyl Cyclases; D005947:Glucose