Schizosaccharomyces pombe glucose/cAMP signaling requires the Hsp90/Git10 chaperone and the Git7 co-chaperone

Abstract

The fission yeast Schizosaccharomyces pombe senses environmental glucose through a cAMP-signaling pathway. Elevated cAMP levels activate protein kinase A (PKA) to inhibit transcription of genes involved in sexual development and gluconeogenesis, including the fbp1⁺ gene, which encodes fructose-1,6-bisphosphatase. Glucose-mediated activation of PKA requires the function of nine git genes (git=glucose insensitive transcription), encoding adenylate cyclase, the PKA catalytic subunit and seven “upstream” proteins required for glucose-triggered adenylate cyclase activation. This thesis describes the cloning and characterization of the git10⁺ gene, which is identical to swo1⁺ and encodes the S. pombe Hsp90 chaperone protein. This discovery is consistent with the previous identification of the Git7 protein as a member of the Sgt1 Hsp90 co-chaperone family. Glucose repression of fbp1⁺ transcription is impaired by both hsp90⁻ and git7⁻ mutant alleles, as well as by chemical inhibition of Hsp90 activity and temperature stress. Unlike the swo1⁻ and git7⁻ ts mutant alleles, the git10-201 allele and git7-93 allele support cell growth at 37º and show no cytokinesis defect, while severely reducing glucose repression of an fbp1-lacZ reporter, suggesting a separation-of-function defect. A physical interaction between Git7 and Hsp90 in S. pombe was also detected and findings in this thesis suggest their involvement in the initial assembly of the cAMP complex.