Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of a trans-acting mutation, dgkR1, which causes a 7-fold elevation of diacylglycerol kinase activity in membranes (Raetz, C. R. H., Kantor, G. D., Nishijima, M., and Jones, M. L. (1981) J. Biol. Chem. 256, 2109-2112) was investigated by direct measurement of diacylglycerol kinase polypeptide by high performance liquid chromatography and by construction of fusions of the dgkA promoter to beta-galactosidase and galactokinase. The dgkR1 mutation was demonstrated to act by increasing the transcription of the structural gene for diacylglycerol kinase, dgkA. Additionally, sn-glycerol-3-phosphate acyltransferase activities were shown to be decreased 30-50% in membranes from dgkR1 mutant strains. Increased diacylglycerol levels occurred when cells were grown on low osmolarity media. This did not affect dgkA expression. In a dgkR+ background, enhanced expression of sn-1,2-diacylglycerol kinase activity in cells containing a high copy number plasmid bearing dgkA decreased sn-1,2-diacylglycerol levels. However, overproduction of diacylglycerol kinase in a dgkR1 genetic background did not affect diacylglycerol levels, suggesting that the dgkR1 mutation affects diacylglycerol metabolism by mechanisms additional to enhancement of dgkA transcription.
 ...
PMID:Regulation of diacylglycerol kinase biosynthesis in Escherichia coli. A trans-acting dgkR mutation increases transcription of the structural gene. 301 52

The topology of Escherichia coli diacylglycerol kinase (DAGK) within the cytoplasmic membrane was elucidated by a combined approach involving both multiple aligned sequence analysis and fusion protein experiments. Hydropathy plots of the five prokaryotic DAGK sequences available were uniform in their prediction of three transmembrane segments. The hydropathy predictions were experimentally tested genetically by fusing C-terminal deletion derivatives of DAGK to beta-lactamase and beta-galactosidase. Following expression, the enzymatic activities of the chimeric proteins were measured and used to determine the cellular location of the fusion junction. These studies confirmed the hydropathy predictions for DAGK with respect to the number and approximate sequence locations of the transmembrane segments. Further analysis of the aligned DAGK sequences detected probable alpha-helical N-terminal capping motifs and two amphipathic alpha-helices within the enzyme. The combined fusion and sequence data indicate that DAGK is a polytopic integral membrane protein with three transmembrane segments with the N terminus of the protein in the cytoplasm, the C terminus in the periplasmic space, and two amphipathic helices near the cytoplasmic surface.
 ...
PMID:Membrane topology of Escherichia coli diacylglycerol kinase. 807 Dec 24