The isolation of a temperature-sensitive mutant of E. coli K12 whose active transport of amino acids and sugars is not coupled to metabolic energy at 420 is described. This The ecfta mutation has been mapped to be in the 54.5-to 60-min region of the E. coli chromosome map. Possible interactions between the metC mutation and the mutated energy coupling factor protein are discussed.The molecular mechanisms by which metabolic energy is coupled to active transport in bacteria have been a subject of considerable interest (1-5). In the Escherichia coli membrane vesicle system the oxidation of D-lactate to pyruvate facilitates the transport of a wide variety of amino acids and sugars against a concentration gradient (1, 6). In whole cells the main energy source utilized for aerobic transport comes from respiration and the generation or utilization of ATP does not seem to be involved (7,8). On the other hand, cells apparently utilize the energy derived from the hydrolysis of ATP for anaerobic transport, as demonstrated in studies on mutants defective in the CaMg-ATPase (7, 9). The form of the metabolic energy, whether it be a high-energy intermediate of oxidative phosphorylation, an energized membrane state, or some other form, has not yet been determined (2, 10-12).In this paper we describe a mutant that is temperaturesensitive in a pleiotropic manner for the active transport of amino acids and sugars and is altered in a component energy coupling factor (ECF) that is necessary for the coupling of metabolic energy to transport. We also present evidence that a derivative of methionine may be interacting with the altered protein.
MATERIALS AND METHODSBacterial Strains. All strains used were of E. coli K12 and are listed in Table 1