Inhibition of the SOS response of Escherichia coli by the Ada protein

Induction of the alkylation-inducible aidB gene of Escherichia coli by cytoplasmic acidification and N-ethylmaleimide

We have studied the effects of changes in intracellular pH and the influence of thiol reagents on the induction of the DNA damage-inducible genes of Escherichia coli, aidB, alkA, and alkB. Under aerobic conditions in the absence of alkylating agents aidB, but not alkA or alkB, was induced by an acidification of cytoplasm or by treatment with the sulfhydryl reagent N-ethylmaleimide. Alkaline shift and thiosalicyclic acid did not affect the induction of aidB and alkB. The induction of alkA increased under the alkaline shift but not in the case of treatment with reducing agents. Compared with the aidB gene, a component of the SOS system, the sulA (sfiA) gene, responded to changes in cytoplasmic pH and in the level of intracellular thiols in an opposite way. SulA induction was observed under alkaline shift and after treatment with thiosalicylic acid.

Mutation enhancing effect of o-vanillin in the lacZ gene of Escherichia coli: characterization of mutational spectrum

The enhancing effect of o-vanillin (2-hydroxy-3-methoxybenz-aldehyde) on mutations induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was characterized with mutational specificity. The mutational spectrum of MNNG-induced mutations in the presence of o-vanillin was compared with that in the absence of o-vanillin by means of a series of mutant lacZ genes in E. coli that can detect each of the six types of base substitutions and five kinds of frameshift events. In the absence of o-vanillin, the mutational spectrum induced by MNNG consisted mainly of G.C-->A.T transitions and, to a lesser extent, -1(G.C) frameshift mutations. By adding o-vanillin at 75 micrograms/plate, a marked enhancement was observed in two transitions, G.C-->A.T and A.T-->G.C, and in two frameshift mutations, +1(G.C) and -1(G.C). Only a small change was observed in the -2(C.G-G.C) fraction. Regarding the MNNG-induced frameshifts at the A.T base pair, the +1(A.T) frameshift was much more enhanced by o-vanillin than the -1(A.T) frameshift.

Runaway–Replication Plasmids as Tools to Produce Large Quantities of Proteins from Cloned Genes in Bacteria

Here we review the properties and uses of runaway-replication vectors, a class of versatile plasmids discovered and developed in Escherichia coli. They are based on the IncFII plasmid, R1, in which an antisense RNA (CopA RNA) negatively controls the formation of a protein that is rate-limiting for replication. The copy number of the plasmid is determined by the balance between the rates of formation of CopA RNA and RepA mRNA. A small increase in the rate of formation of the latter drastically reduces the rate of formation of CopA RNA due to convergent transcription, which may lead to a total loss of copy number control (runaway replication), resulting in massive DNA amplification, and plasmid copy numbers up to 1000 per genome. Since this amplification occurs in the presence of protein synthesis, the protein that is encoded by a cloned gene can also be amplified, and may constitute 10-50% of the total protein.

Altered induction of the adaptive response to alkylation damage in Escherichia coli recF mutants

Escherichia coli recF mutants are hypermutable when treated with methyl methanesulfonate (G. C. Walker, Mol. Gen. Genet. 152:93-103, 1977). In this study, methylation hypermutability of recF mutant strains was examined, and it was found that recF+ is required for normal induction of the adaptive response to alkylation damage. Although this regulatory effect of recF mutations results in reduced levels of enzymes that specifically repair methyl lesions in DNA, it only partially explains the hypermutability. Further examination showed that methylation hypermutability of recF mutant strains required a functional umuDC operon, a component of the SOS response. These results lead to the hypothesis that methylation hypermutability results from the effects of recF mutations on the induction of both the SOS response and the adaptive response.