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Author Notes:

Address correspondence to: Judith L. Fridovich-Keil, Dept. of Human Genetics, Rm. 325.2 Whitehead Bldg., 615 Michael St, Atlanta, GA 30322 USA, (tel) 404−727−3924, (FAX) 404−727−3949, (email) jfridov@emory.edu

ACKNOWLEDGMENTS The authors would like to recognize the many helpful contributions of all members of the Fridovich-Keil lab, and also gratefully acknowledge funding support from the National Institute of Health in the form of NRSA Award DK074297 (to K. Ross) and R01 Awards DK059904 and DK046403 (to J. Fridovich-Keil)


Research Funding:

National Institute of Diabetes and Digestive and Kidney Diseases : NIDDK

Funding support from the National Institute of Health in the form of NRSA Award DK074297 (to K. Ross) and R01 Awards DK059904 and DK046403 (to J. Fridovich-Keil)


  • galactose
  • galactosemia
  • yeast
  • gal-1P
  • GALT
  • GALE
  • GALK

Distinct Roles Of Galactose-1P In Galactose-mediated Growth Arrest Of Yeast Deficient In Galactose-1P Uridylyltransferase (GALT) and UDP-galactose 4'-epimerase (GALE)


Journal Title:

Molecular Genetics and Metabolism


Volume 93, Number 2


, Pages 160-171

Type of Work:

Article | Post-print: After Peer Review


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.

Copyright information:

© 2007 Elsevier Inc. All rights reserved.

This is an Open Access work distributed under the terms of the Creative Commons Attribution-NonCommerical-NoDerivs 3.0 Unported License (http://creativecommons.org/licenses/by-nc-nd/3.0/).

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