1997 REGULATION OF HEME BIOSYNTHESIS IN S ..
In Salmonella typhimurium and Escherichia coli, the hemA gene encodes the enzyme glutamyl-tRNA reductase, which catalyzes the first committed step in heme biosynthesis. We report that when heme limitation is imposed on cultures of S. typhimurium, glutamyl-tRNA reductase (HemA) enzyme activity is increased 10- to 25-fold. Heme limitation was achieved by a complete starvation for heme in hemB, hemE, and hemH mutants or during exponential growth of a hemL mutant in the absence of heme supplementation. Equivalent results were obtained by both methods. To determine the basis for this induction, we developed a panel of monoclonal antibodies reactive with HemA, which can detect the small amount of protein present in a wild-type strain. Western blot (immunoblot) analysis with these antibodies reveals that the increase in HemA enzyme activity during heme limitation is mediated by an increase in the abundance of the HemA protein. Increased HemA protein levels were also observed in heme-limited cells of a hemL mutant in two different E. coli backgrounds, suggesting that the observed regulation is conserved between E. coli and S. typhimurium. In S. typhimurium, the increase in HemA enzyme and protein levels was accompanied by a minimal (less than twofold) increase in the expression of hemA-lac operon fusions; thus HemA regulation is mediated either at a posttranscriptional step or through modulation of protein stability.
Regulation of heme biosynthesis in Escherichia coli
Although regulation of heme biosynthesis is not well studied in ..
This review focuses on the known regulatory mechanisms in non-phototrophic bac-teria involved in the control of the formation of the heme biosynthetic apparatus.
Regulation of Methionine Biosynthesis in Escherichia coli: ..
Focusing on the well investigated bacteria Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhimurium the involved environ-mental stimuli, employed transcriptional regula-tors and promoter structures as well as the role of protein stability are described.