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Luria-Bertani broth supports Escherichia coli growth to an optical density at 600 nm (OD(600)) of 7. Surprisingly, however, steady-state growth ceases at an OD(600) of 0.3, when the growth rate slows down and cell mass decreases. Growth stops for lack of a utilizable carbon source. The carbon sources for E. coli in Luria-Bertani broth are catabolizable(More)
We present and evaluate the SOS chromotest, a bacterial test for detecting DNA-damaging agents. It is a colorimetric assay based on the induction by these agents of the SOS function sfiA, whose level of expression is monitored by means of a sfiA::lacZ operon fusion. The response is rapid (a few hours), and does not require survival of the tester strain.(More)
Blocks in DNA replication cause a rapid arrest of cell division in Escherichia coli. We have previously established that the function SfiA (SulA), induced under these conditions as part of the SOS response, is involved in this inhibition of division. To separate the effects of SfiA from those of other SOS functions, we have constructed a plac-sfiA operon(More)
Escherichia coli double mutants (sodA sodB) completely lacking superoxide dismutase (SOD) have greatly enhanced mutation rates during aerobic growth. Single mutants lacking manganese SOD (MnSOD) but possessing iron SOD (FeSOD) have a smaller increase, and single mutants lacking FeSOD but possessing MnSOD do not show such an increase. The enhancement of(More)
The enzyme S-adenosylmethionine (SAM) synthetase, the Escherichia coli metK gene product, produces SAM, the cell's major methyl donor. We show here that SAM synthetase activity is induced by leucine and repressed by Lrp, the leucine-responsive regulatory protein. When SAM synthetase activity falls below a certain critical threshold, the cells produce long(More)
The Escherichia coli proteins DksA, GreA, and GreB are all structural homologs that bind the secondary channel of RNA polymerase (RNAP) but are thought to act at different levels of transcription. DksA, with its co-factor ppGpp, inhibits rrnB P1 transcription initiation, whereas GreA and GreB activate RNAP to cleave back-tracked RNA during elongational(More)
Cell division is a tightly regulated periodic process. In steady-state cultures of Enterobacteriaceae, division takes place at a well defined cell mass and is strictly coordinated with DNA replication. In wild-type Escherichia coli the formation of cells lacking DNA is very rare, and interruptions of DNA replication arrest cell division. The molecular bases(More)
The heat shock response in Escherichia coli is governed by the concentration of the highly unstable sigma factor sigma 32. The essential protein HflB (FtsH), known to control proteolysis of the phage lambda cII protein, also governs sigma 32 degradation: an HflB-depleted strain accumulated sigma 32 and induced the heat shock response, and the half-life of(More)
The leucine regulon coordinates the expression of several Escherichia coli genes according to the presence of exogenous leucine, which interacts with the lrp gene product, Lrp. We isolated and characterized 22 strains with lambda placMu insertions in Lrp-regulated genes. Lrp and leucine influenced gene expression in a surprising variety of ways. We(More)