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C O Doudney

Publications and source records attributed to C O Doudney.

At least 19 recordsLinked to original sources
PubMed1990

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. After a higher fluence (20 J/m2), an inhibition of replication recovery was revealed. This fluence delays the reinitiation of DNA accumulation in the culture, measured by [14C]thymine incorporation, for 25 min more, in addition to the 20-min recovery period. This finding was confirmed with pulse-labelling studies, which revealed that the higher exposure represses the rates of replication for 45 min before replication at the normal rate reinitiates in the culture. It was proposed that the inhibition of recovery revealed by these investigations is effected by the UV-induction of an active DNA-replication recovery-inhibition process. With the uvrA strain, rate studies revealed that 1.5 J/m2 of UV (a reduced fluence necessary because of the greater sensitivity of the strain) induces a transient inhibition of DNA replication, with considerable recovery following. Exposure to 3.0 J/m2 induces the transient inhibition of replication, followed by massive recovery inhibition after 20 min of incubation. With uvrA recA, both the lower and the higher fluence resulted in an immediate block of replication with no recovery, confirming the recA gene dependency of the recovery process. The decrease in rate of replication comparable to that seen in the uvrA strain after 20 min, and taken as evidence of the function of the recovery-inhibition process, was not seen. The evidence supports the concept that a process somehow triggered by higher UV fluences functions to repress replication temporarily, presumably allowing time for repair processes to take place before replication overruns closely linked pyrimidine dimers on opposite strands to create lethal lesions.

DNA Replication↗
PubMed1989

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. coli WP2 trp showed a similar pattern with chloramphenicol treatment or tryptophan starvation before UV exposure, but only if protein synthesis were blocked by chloramphenicol for 60 min after UV exposure. The results suggest that when recA/lexA-regulon induction is prevented, either by the recA mutation or by inhibition of protein synthesis after UV exposure, death occurs unless the cells are in the resistant state characteristic of bacteria at the end of their DNA replication cycle. With repair-proficient bacteria treated before UV exposure with chloramphenicol, when protein synthesis is not blocked after UV exposure, a marked expansion of the shoulder occurs because of the function of another resistance-conferring mechanism. This mechanism also depends on the recA+ gene since expansion of the shoulder does not occur in recA bacteria when protein synthesis is inhibited before UV exposure.

Cell Survival↗
PubMed1985

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. Rifampin, which blocks DNA-dependent RNA polymerase function, limited drastically expansion of the shoulder and development of the intermediate exponential slope. Bacteria defective in DNA polymerase I (polA) showed only a slight expansion of the shoulder with pretreatment with chloramphenicol. Since certain bacterial plasmids require RNA primer formation for initiation of replication and are not maintained in a polA strain, it is proposed that the chloramphenicol-promoted increase in resistance depends on the formation of multiple numbers of specific resistance episomes (called repairons in view of their role in DNA repair).

Chloramphenicol↗
PubMed1984

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. Nalidixic acid prevented both the changes in survival and mutation. Mutation curves obtained with overnight cultures had three extended sections of little mutation alternating with sections of high mutation. Reincubation for 60 min in fresh medium reduced or eliminated the low-response sections. These reappeared after 80 to 90 min, when DNA had doubled in the culture and before the initial synchronous cell divisions had occurred. Nalidixic acid prevented this reappearance.

Chloramphenicol↗
PubMed1978

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. The ability of a high concentration of rifampicin to limit DNA replication was eliminated by addition of either high or low concentrations of chloramphenicol, indicating that stoichiometric interaction of the antibiotics is not responsible for this effect.

Chloramphenicol↗
PubMed1978

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. With the uvrA strain the increase in shoulder expanse after tryptophan prestarvation was accompanied by greatly increased 2DM but no change in 1DM. Preincubation with chloramphenicol induced an even greater increase in 2DM response than amino acid prestarvation. Nalidixic acid, which prevents DNA accumulation, eliminated the response.

Dose-Response Relationship, Radiation↗
PubMed1976

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. The third section demonstrates an increased rate of mutagenesis and suggests the induction of two lesions in proximity which result in additional mutations. Split-exposure studies support the inducible nature of the SOS function and suggest that mutation frequency decline (MFD) is due to exicion resulting from or related to the prevention of SOS induction by inhibition of protein synthesis. Preirradiation tryptophan starvation of the uvr+ strain for 30 min decrease MFR in the first and second sections of the curve. Reduction of MFR in the third section requires more prestarvation time and is blocked by nalidixic acid. The decreased MFR of the first and second sections ascribed to promotion of postirradiation MFD based on excision and that of third section to completion of the chromosome during the prestarvation period.

Bacterial Proteins↗
PubMed1974

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. One is ribonucleic acid dependent and is inhibited by streptolydigin. This ribonucleic acid-dependent mechanism appears to be absent in wild-type and RecA E. coli B/r strains.

Agar↗
PubMed1974

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., after postirradiation lag periods of 45 min or more). Neither the absence of thymine nor the absence of tryptophan prevented LOP of the damage to DNA replication, suggesting that neither DNA replication nor protein synthesis is necessary for the process. These findings suggest that attempted initiation of DNA replication results in transformation of pyrimidine damage into permanent damage to chromosome structure at the reinitiation site.

Carbon Radioisotopes↗
PubMed1973

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. coli B/r. However, with the repair-deficient strains, both the shoulder and slope of the survival curve are affected. We investigated the effect of UV irradiation on DNA synthesis in Hcr(-) bacteria and found that pre-irradiation inhibition of protein synthesis increases UV resistance of DNA replication in this strain also. The results suggest that inhibition of protein synthesis before irradiation increases UV resistance in E. coli B/r by a mechanism which is independent of both the excision and recombination repair systems.

Arabinose↗