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Eukaryotic Cell, August 2002, p. 558-567, Vol. 1, No. 4
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.4.558-567.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Schizosaccharomyces pombe Git7p, a Member of the Saccharomyces cerevisiae Sgt1p Family, Is Required for Glucose and Cyclic AMP Signaling, Cell Wall Integrity, and Septation

Kevin Schadick,1 H. Matthew Fourcade,1,{dagger} Peter Boumenot,1 Jeffrey J. Seitz,1 Jennifer L. Morrell,2,3 Louise Chang,2,3,{ddagger} Kathleen L. Gould,2,3 Janet F. Partridge,4 Robin C. Allshire,4 Katsumi Kitagawa,5,3 Phil Hieter,5 and Charles S. Hoffman1*

Biology Department, Boston College, Chestnut Hill, Massachusetts 02467,1 Howard Hughes Medical Institute,2 Department of Cell Biology, School of Medicine, Vanderbilt University, Nashville, Tennessee 37232,3 MRC Human Genetics Unit, Western General Hospital, Edinburgh EH4 2XU, Scotland,4 Center for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada5

Received 26 November 2001/ Accepted 29 April 2002

The Schizosaccharomyces pombe fbp1 gene, encoding fructose-1,6-bisphosphatase, is transcriptionally repressed by glucose. Mutations that confer constitutive fbp1 transcription identify git (glucose-insensitive transcription) genes that encode components of a cyclic AMP (cAMP) signaling pathway required for adenylate cyclase activation. Four of these genes encode the three subunits of a heterotrimeric G protein (gpa2, git5, and git11) and a G protein-coupled receptor (git3). Three additional genes, git1, git7, and git10, act in parallel to or downstream from the G protein genes. Here, we describe the cloning and characterization of the git7 gene. The Git7p protein is a member of the Saccharomyces cerevisiae Sgt1p protein family. In budding yeast, Sgt1p associates with Skp1p and plays an essential role in kinetochore assembly, while in Arabidopsis, a pair of SGT1 proteins have been found to be involved in plant disease resistance through an interaction with RAR1. Like S. cerevisiae Sgt1p, Git7p is essential, but this requirement appears to be due to roles in septation and cell wall integrity, which are unrelated to cAMP signaling, as S. pombe cells lacking either adenylate cyclase or protein kinase A are viable. In addition, git7 mutants are sensitive to the microtubule-destabilizing drug benomyl, although they do not display a chromosome stability defect. Two alleles of git7 that are functional for cell growth and septation but defective for glucose-triggered cAMP signaling encode proteins that are altered in the highly conserved carboxy terminus. The S. cerevisiae and human SGT1 genes both suppress git7-93 but not git7-235 for glucose repression of fbp1 transcription and benomyl sensitivity. This allele-specific suppression indicates that the Git7p/Sgt1p proteins may act as multimers, such that Git7-93p but not Git7-235p can deliver the orthologous proteins to species-specific targets. Our studies suggest that members of the Git7p/Sgt1p protein family may play a conserved role in the regulation of adenylate cyclase activation in S. pombe, S. cerevisiae, and humans.

* Corresponding author. Mailing address: Boston College, Biology Department, Higgins Hall 401B, Chestnut Hill, MA 02467. Phone: (617) 552-2779. Fax: (617) 552-2011. E-mail: hoffmacs{at}bc.edu.

{dagger} Present address: Comparative Genomics Group, Joint Genome Institute, Walnut Creek, CA 94598.

{ddagger} Present address: Division of Medical Genetics, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109-0650.

§ Present address: Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, TN 38105.

Eukaryotic Cell, August 2002, p. 558-567, Vol. 1, No. 4
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.4.558-567.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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