ISOLATION AND PROPERTIES OF A MUTANT OF ESCHERICHIA-COLI WITH AN INSERTIONAL INACTIVATION OF THE USPA GENE, WHICH ENCODES A UNIVERSAL STRESS PROTEIN

Cells of Escherichia coli increase greatly the synthesis of a small cy toplasmic protein as soon as the cell growth rate falls below the maxi mal growth rate supported by the medium, regardless of the condition i nhibiting growth. The gene, designated uspA (universal stress protein A), encoding this protein has been cloned and mapped, and its nucleoti de sequence has been determined (T. Nystrom and F. C. Neidhardt, Mol. Microbiol. 6:3187-3198, 1992). We now report the isolation of an E. co li mutant defective in UspA synthesis because of insertional inactivat ion of the corresponding gene. Analysis of such a mutant demonstrated that it grows at a rate indistinguishable from that of the isogenic pa rent but lags significantly when diluted into fresh medium, regardless of the carbon source included. In addition, the mutant exhibits a dia uxic type of growth when grown on certain single substrates, such as g lucose and gluconate. This growth phenotype was found to be the result of abnormal metabolism of the carbon source (e.g., glucose) accompani ed by excretion into the medium of acetate. The diauxic type of growth may be attributed to the failure of cells to form acetyl coenzyme A s ynthetase and to form isocitrate lyase and malate synthase of the glyo xalate bypass, needed for the assimilation of the produced acetate, un til glucose or gluconate has been completely exhausted. The uspA mutan t appears to dissimilate glucose at an elevated rate that is not comme nsurate with its biosynthetic processes. These results suggest that th e role of protein UspA may be to modulate and reorganize the flow of c arbon in the central metabolic pathways of E. coli during growth arres t.