Rescue by chloramphenicol and rifampicin of UV-irradiated lon, exrA and recA mutants of Escherichia coli K12

The effect of temporary treatment with chloramphenicol or rifampicin on the survival of UV irradiated cells of selected Escherichia coli K12 radiation sensitive mutants was examined. Increased survival resulted for both exrA and recA mutants, and also for the unsuppressed lon mutant, but cells of the parent strain and the recB mutant were not rescued. This contrasts with our earlier finding that after exposure of the bacteria to γ-rays, chloramphenicol treatment rescued the exrA and lon mutants but not the recA mutant. We now report that an exrA recA double mutant was rescued by chlramphenicol after UV radiation, but not after anaerobic ionizing radiation. Inclusion of inhibitors of uvrA governed repair, caffeine and 8-methoxypsoralen (8-MOP), in the incubation medium containing chloramphenicol, did not reduce the rescue of the exrA or recA mutants, although caffeine eliminated rescue of the lon mutant, which was itself unaffected by 8-MOP. However it is concluded that chlormaphenicol rescue of the exrA and recA mutants after UV radiation was not entirely independent of the excision-repair process, since the uvrA recA and uvrA exrA double mutants were not rescued by this treatment.     

Dithiothreitol pretreatment and inducible repair in UV-irradiated Escherichia coli K12 cells

The UV radiation survival of several Escherichia coli K12 strains was measured after pretreatment of the cells with dithiothreitol (DTT). In DNA repair-competent cells (AB1157), UV survival was enhanced (ER = 1.2) after pretreating cells for 1.0 h using 10 mmol dm-3 DTT and then incubating the cells for 1.5 h in buffer before UV irradiation. Similar experiments using the excision repair mutant, AB1886uvrA6, or the recombination repair and SOS-deficient mutant, AB2462recA, strains did not show enhanced UV survival. None of the E. coli strains tested were protected against UV killing by simultaneous treatment with DTT (10 mmol dm-3). These results, and the fact that incubation in chloramphenicol removed the wild-type response in DTT-pretreated, UV-irradiated cells, suggest that the observed UV radioprotection was a result of inducible enzymatic repair processes such as recA-dependent repair. The proposed stimulus for inducible repair in these cells is DNA damage caused by intracellular hydroxyl radicals arising from thiol oxidation. The involvement of oxygen radicals in the induction pathway is supported by results that showed superoxide dismutase and catalase could inhibit a portion (one-third) of the inducible repair.     

recA (Srf) suppression of recF deficiency in the postreplication repair of UV-irradiated Escherichia coli K-12.

The mechanism by which recA (Srf) mutations (recA2020 and recA801) suppress the deficiency in postreplication repair shown by recF mutants of Escherichia coli was studied in UV-irradiated uvrB and uvrA recB recC sbcB cells. The recA (Srf) mutations partially suppressed the UV radiation sensitivity of uvrB recF, uvrB recF recB, and uvrA recB recC sbcB recF cells, and they partially restored the ability of uvrB recF and uvrA recB recC sbcB recF cells to repair DNA daughter-strand gaps. In addition, the recA (Srf) mutations suppressed the recF deficiency in the repair of DNA double-strand breaks in UV-irradiated uvrA recB recC sbcB recF cells. The recA2020 and recA801 mutations do not appear to affect the synthesis of UV radiation-induced proteins, nor do they appear to produce an altered RecA protein, as detected by two-dimensional gel electrophoresis. These results are consistent with the suggestion (M. R. Volkert and M. A. Hartke, J. Bacteriol. 157:498-506, 1984) that the recA (Srf) mutations do not act by affecting the induction of SOS responses; rather, they allow the RecA protein to participate in the recF-dependent postreplication repair processes without the need of the RecF protein.     

Occurrence and loss of alkali-labile sites in newly synthesized DNA of UV-irradiated Escherichia coli K12

In pulse-labelled DNA of ultraviolet-irradiated E. coli, alkali-labile sites were detected. They do not occur in undamaged cells. These sites are produced in wild-type cells as well as in uvrA, uvrB and recA derivatives. Restoration of the synthesis of DNA molecules free of alkali-labile sites requires recA products and involves also uvrA and uvrB products. The chemical nature of alkali-labile sites and their biological function are obscure. They might be stretches of RNA that traverse the lesions, blocking DNA replication and priming recA-dependent DNA replication.     

Participation of rec genes of Escherichia coli K 12 in W-reactivation of UV-irradiated phage lambda.

The effect of the recombinational deficiency on W-reactivation of UV-damaged phage lambda was explored. In this paper we show that W-reactivation is reduced by the recB21 and recF143 mutations after bleomycin (BM) and UV treatment. Combination of these mutations in the recB21recF143 double mutant blocks W-reactivation completely after BM induction, but leaves residual W-reactivation ability after UV-irradiation, which is abolished by the introduction of uvrB deficiency (delta(uvrB-chlA]. W-reactivation has been rendered constitutive in recB21C22sbcB15, but the efficiency of reactivation remained virtually constant over the range of BM and UV doses, indicating the role of the RecBC(D) enzyme in W-reactivation.     

recA+ gene-dependent regulation of a uvrD::lacZ fusion in Escherichia coli K12

The expression of the Escherichia coli uvrD gene was studied with a uvrD::Mud(Aprlac) insertion mutant. The results indicate that it is inducible by DNA damaging agents in a recA+ gene-dependent manner.     

NAD-dependent Recovery of Cell Division in UV-irradiated Escherichia coli B and Lon- Mutant of Escherichia coli K-12

We found that both benzyl isothiocyanate (ITC) and phenyl ITC inhibited respiration in the mitochondria in an electrophilic reaction-dependent manner. ITC-induced mitochondrial swelling and cytochrome c release were prevented by cyclosporin A, indicating that they are mediated through the ITC moiety-dependent reaction to critical thiol groups for the opening of membrane permeability transition-dependent pores.     

Chromosome transfer and Hfr formation by F in rec+ and recA strains of Escherichia coli K12.

We attempted to assess the role of Hfr clones in chromosome transfer by F⁺ populations. We thought that any Hfr-independent component of fertility might be affected to a different extent by the recA mutation than was the Hfr component. However, the rate of Hfr formation and the efficiency of chromosome transfer were reduced to an equal extent (× 100-fold) by the recA mutation. Such experiments therefore provide no evidence for an Hfr-independent component. It appeared that Type II strains, which were thought to suffer a defect in Hfr formation, actually produced fertile clones but had a secondary defect which affected the persistence of these clones. Thus, evidence from Type II strains is also not useful for examining the quantitative contribution of Hfr cells to F⁺ transfer.     

Dissociation of tsl-tif-Induced Filamentation and recA Protein Synthesis in Escherichia coli K-12

In Escherichia coli, expression of the tif-1 mutation (in the recA gene) induces the "SOS response" at 40 degrees C, including massive synthesis of the recA(tif) protein, cell filamentation, appearance of new repair and mutagenic activities, and prophage induction. Expression of the tsl-1 mutation (in the lexA gene) induces massive synthesis of the recA protein and cell filamentation at 42 degrees C, although other SOS functions are not induced. In this paper we show that the septation inhibition induced in tif and tsl strains at 42 degrees C is not due to the presence of a high concentration of recA protein since (i) no recA mutants (相似文献   

Effect of flash photoreactivation on Escherichia coli recA induction by ultraviolet light

Excision-deficient Escherichia coli, carrying the gene for the photolyase on a multicopy plasmid, were irradiated with ultraviolet (UV) light then photoreactivated by illumination delivered from a camera flash unit. Such instantaneous illumination monomerizes only cyclobutane pyrimidine dimers already bound by the photolyase. Whereas the lethal effect of UV light and the number of C-to-T transition-type mutations induced by UV irradiation were both significantly reduced by subsequent irradiation with a single flash of light, single-flash photoreactivation did not reverse the induction of the recA gene by UV light. The results indicate, therefore, that non-photoreactivable DNA lesions play a role in recA induction.