In Escherichia coli, a two-component signal transduction system, consisting of the transmembrane sensor protein ArcB and its cognate cytoplasmic regulatory protein ArcA, controls the expression of genes encoding enzymes involved in aerobic respiration. ArcB belongs to a subclass of sensors that have not only a conserved histidine-containing transmitter domain but also a conserved aspartate-containing receiver domain of the regulator family. ' In Escherichia coli, products of the arcA (min 0) and arcB (min 69.5) genes pleiotropically control the expression of numerous target operons, exerting both positive and negative effects. For instance, expression of the structural genes encoding several dehydrogenases of the flavoprotein class; the cytochrome o complex; and members of the tricarboxylic acid cycle, the glyoxylate shunt, and the pathways for fatty acid degradation are anaerobically repressed (15,17). In contrast, expression of the cydAB operon encoding the 02-scavenging cytochrome d is activated under anoxic conditions (6, 16). As a network, these enzymes are responsible for the efficient generation of metabolic energy by aerobic respiration. ArcA (or SfrA, for sex factor regulation) is also required for expression of the tra (DNA transfer) genes of the F plasmid. In this function, CpxA, instead of ArcB, might act in conjunction with ArcA (18,30,32,33,38 (21), and in the case of the sensor FrzE of Myxococcus xanthus, an Asp residue(s) has been shown to undergo autophosphorylation (26). In contrast, ArcA is a typical regulator protein, with only the receiver domain containing conserved Asp residues at positions 11 and 54 as potential sites for transphosphorylation by phosphorylated ArcB (ArcB-P) (4,20). In this study, we constructed plasmids for producing and purifying the two proteins 'ArcB (an ArcB lacking the two transmembrane portions in the N-terminal region) and ArcA for the purpose of testing (i) whether ArcB undergoes autophosphorylation at both His and Asp residues and (ii) whether an Asp residue of ArcA can receive a phosphoryl group from ArcB-P.
MATERUILS AND METHODSBacteria, phages, and plasmids. All strains used (XL1-Blue [Stratagene], K38, and ECL594) were derivatives of E. coli K-12. P1 vir phage was used for transductions. To place arcBl in strain K38 with a plasmid (pGP1-2) encoding the T7 polymerase gene (37), the mutant allele in strain ECL594 (15) was cotransduced with a closely linked TnlO (85%). Tetr transductants were selected on LB agar containing tetracycline and purified on the same type of agar. Coinheritance of arcBl was scored for sensitivity to the redox dye toluidine blue o (20). Plasmid pT7-7 was provided by S. Tabor.Growth conditions. For routine cultures, LB medium (1% tryptone, 0.5% yeast extract, 0.5% NaCl) was used. To select Tetr transductants, tetracycline was added at 10 ,ug/ml in LB agar. Ampicillin (100 ,ug/ml) and kanamycin (75 ,ug/ml) were added to LB medium to prevent loss of plasmid vectors bearing a drug resistance marker. To test for dye sensitivity, toluidine bl...