GAL1/YBR020W Summary Help

Standard Name GAL1 1, 2
Systematic Name YBR020W
Feature Type ORF, Verified
Description Galactokinase; phosphorylates alpha-D-galactose to alpha-D-galactose-1-phosphate in the first step of galactose catabolism; expression regulated by Gal4p; GAL1 has a paralog, GAL3, that arose from the whole genome duplication (3, 4, 5 and see Summary Paragraph)
Name Description GALactose metabolism
Chromosomal Location
ChrII:279021 to 280607 | ORF Map | GBrowse
Genetic position: 7 cM
Gene Ontology Annotations All GAL1 GO evidence and references
  View Computational GO annotations for GAL1
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 4 genes
Classical genetics
Large-scale survey
45 total interaction(s) for 29 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 3
  • Affinity Capture-RNA: 3
  • Co-purification: 1
  • PCA: 1
  • Reconstituted Complex: 1
  • Two-hybrid: 2

Genetic Interactions
  • Dosage Lethality: 1
  • Dosage Rescue: 2
  • Negative Genetic: 13
  • Phenotypic Enhancement: 3
  • Phenotypic Suppression: 2
  • Positive Genetic: 6
  • Synthetic Growth Defect: 4
  • Synthetic Rescue: 3

Expression Summary
Length (a.a.) 528
Molecular Weight (Da) 57,944
Isoelectric Point (pI) 6.71
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrII:279021 to 280607 | ORF Map | GBrowse
Genetic position: 7 cM
Last Update Coordinates: 2004-07-16 | Sequence: 1997-01-28
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..1587 279021..280607 2004-07-16 1997-01-28
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | E.C. | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000000224

The Gal1p galactokinase catalyzes the conversion of alpha-D-galactose to galactose-1-phosphate, a key step in galactose catabolism (6, 7). Gal1p is also required for inducible high-affinity galactose uptake, and can function as a weak transcriptional regulator in the absence of Gal3p (8, 7). Gal1p and Gal3p share 90% amino acid similarity, and insertion of just two amino acids (a serine and an alanine) directly after amino acid 164 confers galactokinase activity on transcriptional regulator Gal3p (9). Overexpression of GAL1 results in activation of Gal4p, and gal1 null mutants are unable to grow on galactose as the sole carbon source (10, 11).

All the galactose structural genes (GAL1, GAL10, GAL7, GAL2) are coordinately regulated at the level of transcription in response to galactose by Gal4p, Gal80p, and Gal3p (6, 12, and reviewed in 13). Regardless of carbon source, the Gal4p transcriptional activator is bound as a dimer to upstream activation sites found in the promoters of the GAL genes. In the presence of galactose, Gal3p sequesters the transcriptional repressor Gal80p in the cytoplasm, thereby relieving inhibition of Gal4p and resulting in GAL gene expression (14). In the absence of galactose, Gal80p remains bound as a dimer, to Gal4p, preventing Gal4p from recruiting other factors of the Pol II transcription machinery (reviewed in 13).

Galactokinase is conserved from E. coli to man (10 and reviewed in 15). Mutations in human GALK1, the functional ortholog of yeast GAL1, lead to galactokinase deficiency/galactosemia II (OMIM), characterized by cataract formation due to galactitol accumulation (reviewed in 15).

Last updated: 2006-09-18 Contact SGD

References cited on this page View Complete Literature Guide for GAL1
1) Bassel J and Mortimer R  (1971) Genetic order of the galactose structural genes in Saccharomyces cerevisiae. J Bacteriol 108(1):179-83
2) Douglas HC and CONDIE F  (1954) The genetic control of galactose utilization in Saccharomyces. J Bacteriol 68(6):662-70
3) Giniger E, et al.  (1985) Specific DNA binding of GAL4, a positive regulatory protein of yeast. Cell 40(4):767-74
4) Timson DJ and Reece RJ  (2002) Kinetic analysis of yeast galactokinase: implications for transcriptional activation of the GAL genes. Biochimie 84(4):265-72
5) Byrne KP and Wolfe KH  (2005) The Yeast Gene Order Browser: combining curated homology and syntenic context reveals gene fate in polyploid species. Genome Res 15(10):1456-61
6) De Robichon-Szulmajster H  (1958) Induction of enzymes of the galactose pathway in mutants of Saccharomyces cerevisiae. Science 127(3288):28-9
7) Schell MA and Wilson DB  (1977) Purification and properties of galactokinase from Saccharomyces cerevisiae. J Biol Chem 252(4):1162-6
8) Ramos J, et al.  (1989) Characteristics of galactose transport in Saccharomyces cerevisiae cells and reconstituted lipid vesicles. J Bacteriol 171(6):3539-44
9) Platt A, et al.  (2000) The insertion of two amino acids into a transcriptional inducer converts it into a galactokinase. Proc Natl Acad Sci U S A 97(7):3154-9
10) Bhat PJ, et al.  (1990) Analysis of the GAL3 signal transduction pathway activating GAL4 protein-dependent transcription in Saccharomyces cerevisiae. Genetics 125(2):281-91
11) Bhat PJ and Hopper JE  (1992) Overproduction of the GAL1 or GAL3 protein causes galactose-independent activation of the GAL4 protein: evidence for a new model of induction for the yeast GAL/MEL regulon. Mol Cell Biol 12(6):2701-7
12) Platt A and Reece RJ  (1998) The yeast galactose genetic switch is mediated by the formation of a Gal4p-Gal80p-Gal3p complex. EMBO J 17(14):4086-91
13) Lohr D, et al.  (1995) Transcriptional regulation in the yeast GAL gene family: a complex genetic network. FASEB J 9(9):777-87
14) Peng G and Hopper JE  (2002) Gene activation by interaction of an inhibitor with a cytoplasmic signaling protein. Proc Natl Acad Sci U S A 99(13):8548-53
15) Holden HM, et al.  (2004) Galactokinase: structure, function and role in type II galactosemia. Cell Mol Life Sci 61(19-20):2471-84