Galactose is metabolized in humans and other species by the three-enzyme Leloir pathway comprised of galactokinase (GALK), galactose 1-P uridylyltransferase (GALT), and UDP-galactose 4'-epimerase (GALE). Impairment of GALT or GALE in humans results in the potentially lethal disorder galactosemia, and loss of either enzyme in yeast results in galactose-dependent growth arrest of cultures despite the availability of an alternate carbon source. In contrast, loss of GALK in humans is not life-threatening, and in yeast has no impact on the growth of cultures challenged with galactose. Further, the growth of both GALT-null and GALE-null yeast challenged with galactose is rescued by loss of GALK, thereby implicating the GALK reaction product, gal-1P, for a role in the galactose-sensitivity of both strains. However, the nature of that relationship has remained unclear. Here we have developed and applied a doxycycline-repressible allele of galactokinase to define the quantitative relationship between galactokinase activity, gal-1P accumulation, and growth arrest of galactose-challenged GALT or GALE-deficient yeast. Our results demonstrate a clear threshold relationship between gal-1P accumulation and galactose-mediated growth arrest in both GALT-null and GALE-null yeast, however, the threshold for the two strains is distinct. Further, we tested the galactose-sensitivity of yeast double-null for GALT and GALE, and found that although loss of GALT barely changed accumulation of gal-1P, it significantly lowered the accumulation of UDP-gal, and also dramatically rescued growth of the GALE-null cells. Together, these data suggest that while gal-1P alone may account for the galactose-sensitivity of GALT-null cells, other factors, likely to include UDP-gal accumulation, must contribute to the galactose-sensitivity of GALE-null cells.
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Evidence ID | Analyze ID | Gene/Complex | Systematic Name/Complex Accession | Qualifier | Gene Ontology Term ID | Gene Ontology Term | Aspect | Annotation Extension | Evidence | Method | Source | Assigned On | Reference |
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Evidence ID | Analyze ID | Gene | Gene Systematic Name | Phenotype | Experiment Type | Experiment Type Category | Mutant Information | Strain Background | Chemical | Details | Reference |
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Evidence ID | Analyze ID | Gene | Gene Systematic Name | Disease Ontology Term | Disease Ontology Term ID | Qualifier | Evidence | Method | Source | Assigned On | Reference |
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Evidence ID | Analyze ID | Regulator | Regulator Systematic Name | Target | Target Systematic Name | Direction | Regulation of | Happens During | Regulator Type | Direction | Regulation Of | Happens During | Method | Evidence | Strain Background | Reference |
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Site | Modification | Modifier | Source | Reference |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Assay | Annotation | Action | Modification | Source | Reference | Note |
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Complement ID | Locus ID | Gene | Species | Gene ID | Strain background | Direction | Details | Source | Reference |
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Evidence ID | Analyze ID | Dataset | Description | Keywords | Number of Conditions | Reference |
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