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The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

ABSTRACT: The RAG1 gene of Kluyveromyces lactis encodes a low-affinity glucose/fructose transporter. Its transcription is induced by glucose, fructose, and several other sugars. The RAG4, RAG5, and RAG8 genes are trans-acting genes controlling the expression of the RAG1 gene. We report here the characterization of one of these genes, RAG5. The nucleotide sequence of the cloned RAG5 gene indicated that it encodes a protein that is homologous to hexokinases of Saccharomyces cerevisiae. rag5 mutants showed no detectable hexokinase or glucokinase activity, suggesting that the sugar kinase activity encoded by this gene is the only hexokinase in K. lactis. Both high- and low-affinity transport systems of glucose were affected in rag5 mutants. The defect of the low-affinity component was found to be due to a block of transcription of the RAG1 gene by the hexokinase mutation. In vivo complementation of the rag5 mutation by the HXK2 gene of S. cerevisiae and complementation of hxk1 hxk2 mutations of S. cerevisiae by the RAG5 gene showed that RAG5 and HXK2 were equivalent for sugar-phosphorylating activity but that RAG5 could not restore glucose repression in the S. cerevisiae hexokinase mutants.

SUBMITTER: Prior C

PROVIDER: S-EPMC359921 | biostudies-other | 1993 Jul

REPOSITORIES: biostudies-other

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The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

Prior C C Mamessier P P Fukuhara H H Chen X J XJ Wesolowski-Louvel M M

Molecular and cellular biology 19930701 7

The RAG1 gene of Kluyveromyces lactis encodes a low-affinity glucose/fructose transporter. Its transcription is induced by glucose, fructose, and several other sugars. The RAG4, RAG5, and RAG8 genes are trans-acting genes controlling the expression of the RAG1 gene. We report here the characterization of one of these genes, RAG5. The nucleotide sequence of the cloned RAG5 gene indicated that it encodes a protein that is homologous to hexokinases of Saccharomyces cerevisiae. rag5 mutants showed n ...[more]

PMID: 8321195

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Project description:The analysis of glucose signaling in the Crabtree-positive eukaryotic model organism Saccharomyces cerevisiae has disclosed a dual role of its hexokinase ScHxk2, which acts as a glycolytic enzyme and key signal transducer adapting central metabolism to glucose availability. In order to identify evolutionarily conserved characteristics of hexokinase structure and function, the cellular response of the Crabtree-negative yeast Kluyveromyces lactis to rag5 null mutation and concomitant deficiency of its unique hexokinase KlHxk1 was analyzed by means of difference gel electrophoresis. In total, 2,851 fluorescent spots containing different protein species were detected in the master gel representing all of the K. lactis proteins that were solubilized from glucose-grown KlHxk1 wild-type and mutant cells. Mass spectrometric peptide analysis identified 45 individual hexokinase-dependent proteins related to carbohydrate, short-chain fatty acid and tricarboxylic acid metabolism as well as to amino acid and protein turnover, but also to general stress response and chromatin remodeling, which occurred as a consequence of KlHxk1 deficiency at a minimum 3-fold enhanced or reduced level in the mutant proteome. In addition, three proteins exhibiting homology to 2-methylcitrate cycle enzymes of S. cerevisiae were detected at increased concentrations, suggesting a stimulation of pyruvate formation from amino acids and/or fatty acids. Experimental validation of the difference gel electrophoresis approach by post-lysis dimethyl labeling largely confirmed the abundance changes detected in the mutant proteome via the former method. Taking into consideration the high proportion of identified hexokinase-dependent proteins exhibiting increased proteomic levels, KlHxk1 is likely to have a repressive function in a multitude of metabolic pathways. The proteomic alterations detected in the mutant classify KlHxk1 as a multifunctional enzyme and support the view of evolutionary conservation of dual-role hexokinases even in organisms that are less specialized than S. cerevisiae in terms of glucose utilization.

Dataset Information

The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

Publications

The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

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