DNA-replication recovery inhibition and subsequent reinitiation in UV-radiation-damaged E. coli: a strategy for survival.

Using the incorporation of [14C]thymine to measure DNA accumulation, it was shown that exposure of the B/r strain of Escherichia coli to 10 J/m2 of ultraviolet radiation (UV) inhibits replication for about 20 min, but then resumption of replication occurs. Pulse-labelling with [3H]thymidine after exposure of the WT strain to this fluence confirmed the transient inhibition and recovery of DNA replication. After recovery, the rate of accumulation of DNA in the culture increases, to exceed that of the exponentially growing culture, so that eventually the amount of DNA almost equals that of the unirradiated culture.

Evidence that ultraviolet light-induced DNA replication death of recA bacteria is prevented by protein synthesis in repair-proficient bacteria.

The ultraviolet light (UV) survival curve of Escherichia coli WP10 recA trp is almost biphasic, with a greatly reduced shoulder but demonstrating a transition to a decreased slope with increasing fluences, indicating the presence in the culture of a low frequency of resistant cells. Treatment of the culture with chloramphenicol before UV exposure brought almost all of the cells to a high degree of UV resistance, by bringing them to the end of their DNA replication cycle. The survival curves of the repair-proficient E.

Modification of survival after ultraviolet light exposure in a wild-type and a polA strain of Escherichia coli B/r by preirradiation treatment with chloramphenicol or rifampin.

The shoulder of the UV fluence-survival curve of exponentially growing Escherichia coli B/r WP2 trpE65 was expanded by chloramphenicol pretreatment and an exponential segment with intermediate slope appeared between the shoulder and the final exponential segment. These changes were dependent on DNA replication. The transitions with UV exposure to increased slopes were ascribed to UV inactivation of qualitatively different repair systems, each dependent upon the accumulation in each bacterium of multiple DNA-containing redundant repair components, which must be inactivated before the respective transitions to decreased resistance occur.

Chloramphenicol-promoted increase in resistance to UV damage in Escherichia coli B/r WP2 trpE65: development of the capacity for successful repair of otherwise mutagenic or lethal lesions in DNA.

The ultraviolet radiation survival curve of exponentially growing cultures of Escherichia coli B/r WP2 trpE65 was modified by a short period (20 min) of chloramphenicol treatment before UV exposure, which produced an extended exponential section of intermediate slope between the shoulder and the final exponential slope. More prolonged incubation with chloramphenicol (up to 90 min) resulted in little further extension of the intermediate exponential slope, but caused a progressive expansion of the shoulder region. With each period of chloramphenicol pretreatment, a major surge of mutation to tryptophan independence always occurred after that UV fluence promoting the transition from the shoulder to the intermediate exponential slope of the survival curve, and another major surge occurred after that fluence promoting the transition from the intermediate exponential slope to the final exponential slope.

Modification of UV-induced mutation frequency and cell survival of Escherichia coli B/r WP2 trpE65 by treatment before irradiation.

The UV radiation survival curve of exponentially growing cultures of Escherichia coli B/r WP2 trpE65 was modified by pretreatment for short incubation periods (up to 20 min) with chloramphenicol such that an extended exponential section of intermediate slope appeared between the shoulder and the final exponential slope. Surges of mutation to tryptophan independence occurred with each increase in slope of the survival curve. These surges were separated by extended sections of little mutation.

Modification by preirradiation growth conditions of the shoulder of the UV fluence-survival curve of Escherichia coli B/r WP 2 thy trp and changes in mutagenic response toward tryptophan prototrophy.

The distinct three-section UV fluence-mutation frequency response (MFR) curve demonstrated in Escherichia coli strain B/r WP2 thy trp and its uvrA derivative supports the SOS hypothesis and suggests that trp+ revertants can arise either from isolated lesions (1DM) plus SOS induction or from two lesions in proximity (2DM). Preirradiation growth on arabinose instead of glucose converted the fluence-survival curve from highly shouldered to exponential but did not affect the three-section MFR curve. Prestarvation of the uvrA+ strain for tryptophan, which drastically increases the expanse of the shoulder of the survival curve, greatly decreased both 1DM and 2DM.

Rifampicin and chloramphenicol effects on DNA replication in thymine-prestarved Escherichia coli B/r WP2 thy trp.

When cultures of Escherichia coli B/r WP2 thy trp were prestarved for thymine for 30 min, DNA replication after readdition of thymine was limited to an increase of about 100% in the presence of rifampicin, an antibiotic which inhibits DNA-dependent RNA polymerase. However, chloramphenicol, an antibiotic which blocks protein but not RNA synthesis, did not limit replication. After prolonged thymine prestarvation (55 min) DNA increased only about 50% in the presence of rifampicin, but no such limitation occurred in the presence of chloramphenicol.

Rifampicin and chloramphenicol effects on DNA replication in ultraviolet-damaged Escherichia coli B/r WP2 thy trp.

The antibiotic rifampicin, which blocks specifically RNA synthesis, limited DNA replication in Escherichia coli strain B/r WP2 thy trp after an increase of about 50%, when added to the incubation medium at the time of replication initiation after ultraviolet fluences of 20 J/m2...

Complexity of the ultraviolet mutation frequency response curve in Escherichia coli B/r: SOS induction, one-lesion and two-lesion mutagenesis.

Three distinct sections of the ultraviolet mutation frequency response (MFR) curve toward tryptophan prototrophy have been demonstrated in Excherichia coli B/r WP2 trp thy and its uvrA derivative in log-phase growth in minimal medium. The initial section, which appears fluence-squared, may reflect the necessity, if mutation is to result, for induction of two lesions, one located within the potentially mutated genetic locus and the other damaging deoxyribonucleic acid replication and resulting in inducation of the error-prone SOS repair function. A second linear section is ascribed to the continued induction, after exposure above that sufficient for complete SOS expression, of isolated lesions which lead to mutation in potentially mutated loci.

Loss of photoreversibility of damage to deoxyribonucleic acid replication in ultraviolet-irradiated Escherichia coli B-r thy trp.

Loss of photoreversibility (LOP) of the ultraviolet (UV) damage which prevents reinitiation of deoxyribonucleic acid (DNA) replication occurred with incubation of Escherichia coli B/r thy trp cultures after UV doses of 240, 320, and 400 ergs/mm(2). LOP occurred at the time of reinitiation of DNA replication in the cultures (i.e.

Effect of preirradiation ribonucleic acid synthesis inhibition on resistance to ultraviolet light with resistant and sensitive strains of Escherichia coli B-r.

The ultraviolet resistance of a streptolydigin-susceptible strain of Escherichia coli B/r hcr(-) increased during preirradiation treatment with streptolydigin (an inhibitor of deoxyribonucleic acid-dependent ribonucleic acid polymerase) for 20 min and then remained constant. During preirradiation treatment with chloramphenicol (an inhibitor of protein synthesis), resistance to ultraviolet light increased for 1 to 2 h, and reached a maximal level significantly above that attained in streptolydigin-containing medium. These results suggest that there are two mechanisms that function in Hcr(-) cells during chloramphenicol treatment which contribute to the concomitant ultraviolet resistance enhancement.

Relation between survival and deoxyribonucleic acid replication in ultraviolet-irradiated resistant and sensitive strains of Escherichia coli B-r.

When arabinose-grown Escherichia coli B/r is ultraviolet (UV) irradiated in the logarithmic phase of growth, the dose inactivation curve for both colony formation and deoxyribonucleic acid (DNA) synthesis (based on the relative rates of synthesis) is exponential in nature. When protein synthesis is inhibited before UV-irradiation, both inactivation curves have a large shoulder. Pre-irradiation inhibition of protein synthesis increases considerably the colony-forming ability of a UV-irradiated Hcr(-) and Rec(-) strain of E.