Action at a distance for negative control of transcription of the glpD gene encoding sn-glycerol 3-phosphate dehydrogenase of Escherichia coli K-12

Abstract

sn-Glycerol 3-phosphate (glycerol-P) is a ubiquitous compound that can be used by Escherichia coli and other organisms. Glycerol-P is a direct precursor for phospholipid biosynthesis (33). Glycerol-P and its precursors, when present in excess, are used as carbon and energy sources. The reactions in the catabolic pathways are catalyzed by the proteins encoded by the genes of the glp regulon (23, 24). To maintain a cellular concentration of glycerol-P optimal for phospholipid biosynthesis, organisms must coordinate the levels of the catabolic activities with the levels of the phospholipid biosynthetic activities. Specific negative regulation of the glp regulon is exerted by the glp repressor (GlpR) (22-24). The affinity of GlpR for each glp operator site is reduced upon the binding of glycerol-P, the inducer for the glp regulon (23, 24).The glp genes have been mapped to three different regions on the E. coli chromosome and are arranged in five different operons (24). The glpFKX operon is located near 89 min on the linkage map of E. coli (4, 42, 45). The glpF gene encodes the glycerol diffusion facilitator, a cytoplasmic membrane protein, and the glpK gene encodes the cytoplasmic glycerol kinase. The function of the protein encoded by glpX is unknown. The glpTQ operon and divergently transcribed glpACB operon are located near 51 min (4, 9-11, 21, 24, 44). The glpT gene encodes the cytoplasmic membrane-associated glycerol-P permease required for active transport of glycerol-P into the cytoplasm, and the glpQ gene encodes the periplasmic glycerophosphodiesterase that catalyzes the hydrolysis of glycerophosphodiesters to glycerol-P and an alcohol. The glpACB operon encodes the three subunits of anaerobic glycerol-P dehydrogenase. Under anaerobic growth conditions, this enzyme is essential for dissimilation of glycerol-P.The glpD gene and divergently transcribed glpEGR operon are located near 77 min (4, 24). The glpEGR genes encode the specific repressor for the glp regulon and two other proteins (GlpE and GlpG) with unknown functions (36,38,49). The glpD gene encodes the aerobic glycerol-P dehydrogenase associated with the cytoplasmic membrane (3, 37). Under aerobic conditions, this dehydrogenase catalyzes the oxidation of glycerol-P to dihydroxyacetone phosphate with the concurrent formation of reduced flavin adenine dinucleotide used in the respiratory chain. Anaerobic repression of glpD expression is mediated by the two-component regulatory system encoded by arcA and arcB (19).Lin and coworkers found that the glpD operon was controlled more tightly by GlpR than was either the glpTQ or glpFKX operon (30-, 26.5-, and 3.2-fold, respectively [12]). This conclusion was reached after measuring the activities of enzymes encoded by these genes (glycerol-P dehydrogenase, glycerol-P permease, and glycerol kinase) in extracts of a strain harboring a thermolabile glp repressor after growth at various temperatures (12). In contrast, it was recently found that the glpFKX operon was more sensitive than the glpD operon to represso...

Action at a distance for glp repressor control of glpTQ transcription in Escherichia coli K‐12

“…Introduction of an ihfA deletion into strains with glpDor glpK-lacZ fusions did not influence glp repressormediated repression of these fusions (Yang and Larson, 1996). However, deletion of the accessory protein HU reduced repression of glpD threefold, but only in the presence of the remote glpD operators (Yang and Larson, 1996).…”

“…Remote operator sites located about 400 bp away from the proximal operators contribute additionally to repression of both glpT and glpD (Yang and Larson, 1996). The remote operators are also present in multiple copies, but are not directly repeated as is the case for the promoter-proximal operators (the distances between the centres of symmetry of the remote operators O T 1 to O T 3 and O D 3 to O D 4 are 33 bp and 41 bp, respectively).…”

“…Remote operators are functional when separated by more than 1000 bp from the proximal operators, indicating that DNA is able to form protein-mediated loops at long range, much like eukaryotic enhancers Gralla and Collado-Vides, 1996;Mü ller et al, 1996). A repression loop involving GlpR and operators separated by 400 bp was recently implicated in repression of the glpD operon (Yang and Larson, 1996).…”

“…1). This is a relatively weak glp operator region in view of the fact that a higher concentration of GlpR was needed for protection in comparison with glpD or glpF operators, which are protected at less than 1 nM GlpR (Weissenborn et al, 1992;Yang and Larson, 1996 (Fig. 1).…”

“…Recently it was found that binding of HU increased (by several fold) repression of both the gal P2 promoter (Aki et al, 1996) and the glpD operon (Yang and Larson, 1996). In these cases, HU presumably assists repressormediated DNA loop formation involving operators separated by 113 and 400 bp, respectively.…”