Isocitrate lyase of the yeast Kluyveromyces lactis is subject to glucose repression but not to catabolite inactivation.
KlICL1, encoding the isocitrate lyase of Kluyveromyces lactis, was isolated by complementation of the Saccharomyces cerevisiae icl1 deletion mutant. Sequence analysis revealed an open reading frame of 1626 nucleotides encoding a protein with 542 amino acids. The deduced protein shows extensive homologies to isocitrate lyases from various organisms, with an overall identity of 69% to the enzyme from S. cerevisiae. The KlICL1 gene has two major transcription start-points, located at -113 bp and -95 bp relative to the ATG translation start codon. The gene is expressed on ethanol medium only in respiratory-competent cells. Transcription is repressed by glucose. Mutants carrying a Klcat8 deletion lack the ability to derepress KlICL1 transcription. A Klicl1 deletion mutant does not grow on ethanol medium and lacks any isocitrate lyase activity. A strain lacking the gene KlFBP1, which encodes the gluconeogenic enzyme fructose 1,6-bisphosphatase, lacks the ability to grow on non-fermentable carbon sources. This implies that K. lactis does not contain additional isoenzymes catalyzing either of the reactions. Enzyme assays revealed that neither KlIcl1p nor KlFbp1p are subject to catabolite inactivation. However, the respective enzymes from S. cerevisiae are efficiently inactivated when expressed in K. lactis. Thus, despite the extensive sequence similarities of the enzymes involved, non-fermentative carbohydrate metabolism in the two yeasts displays distinct regulatory properties.
Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, 33006 Oviedo, Spain.
M Luz
ML
López
Begoña
B
Redruello
Eva
E
Valdés
Fernando
F
Moreno
Jürgen J
JJ
Heinisch
Rosaura
R
Rodicio
D019342:Acetic Acid / Q000378:metabolism; D000595:Amino Acid Sequence; D004789:Enzyme Activation / Q000235:genetics; D000431:Ethanol / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005822:Genetic Vectors; D005947:Glucose / Q000378:metabolism*; D005990:Glycerol / Q000378:metabolism; D007522:Isocitrate Lyase / Q000037:antagonists & inhibitors* / Q000235:genetics; D007716:Kluyveromyces / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
D005656:Fungal Proteins; D000431:Ethanol; D007522:Isocitrate Lyase; D005947:Glucose; D005990:Glycerol; D019342:Acetic Acid