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B A Bridges

Publications and source records attributed to B A Bridges.

At least 73 records · Page 4Linked to original sources
PubMed1990

An instance of clinical radiation morbidity and cellular radiosensitivity, not associated with ataxia-telangiectasia.

A 14-year-old boy received standard induction chemotherapy for acute lymphoblastic leukaemia followed by standard dose cranial radiation prophylaxis (18 Gy). Severe chemosensitivity and acute radiation reactions occurred and he died at 8 months from late radiation damage. In vitro radiobiological studies of the boy's fibroblasts in culture demonstrated an enhanced radiosensitivity indistinguishable from ataxia-telangiectasia (A-T) cells. However, unlike A-T cells, DNA synthesis following irradiation was inhibited in a normal manner. This patient represents yet another example of extreme radiosensitivity, and the possibility of clinical prediction in the future is discussed.

Adolescent↗
PubMed1989

Studies on the ability of smoke from different types of cigarettes to induce DNA single-strand breaks in cultured human cells.

In this paper we report preliminary studies using alkaline elution to examine the incidence of DNA-strand breakage in human lung cells exposed to smoke/phosphate-buffered saline generated from cigarettes of different tar contents and filter status. The majority of the DNA breaks induced were abolished by catalase indicating a role for active oxygen species. The incidence of breaks did not correlate with the tar content of the cigarettes. The presence of a filter in the cigarette reduced the TPM concentration of the mainstream smoke but did not reduce the number of single-strand breaks occurring in DNA after exposure to smoke/PBS. This last parameter was however reduced if the filter was ventilated.

Catalase↗
PubMed1989

Non-mutability by ultraviolet light in uvrD recB derivatives of Escherichia coli WP2 uvrA is due to inhibition of RecA protein activation.

The deficiency in UV mutagenesis in uvrD3 recB21 strains of E. coli is almost completely overcome by constitutive activation of RecA protein and expression of the SOS system (by recA730 or 43 degrees C treated recA441 lexA71). When SOS was expressed but RecA protein not self-activated (recA441 lexA71 at 30 degrees C), uvrD3 recB21 still reduced UV mutagenesis at low doses. The uvrD3 recB21 combination is therefore inhibiting activation of RecA protein. It is suggested that the DNA unwinding activity of the products of the uvrD and recB genes may be involved in generating single-stranded DNA needed to activate RecA protein both for the cleavage of LexA repressor and for a further role in UV mutagenesis.

DNA Repair↗
PubMed1989

Spontaneous and UV-induced mutations in Escherichia coli K-12 strains with altered or absent DNA polymerase I.

The induction of mutations to valine resistance and to rifampin resistance occurs after UV irradiation in bacteria carrying a deletion through the polA gene (delta polA), showing that DNA polymerase I (PolI) is not an essential enzyme for this process. The PolI deletion strain showed a 7- to 10-fold-higher spontaneous mutation frequency than the wild type. The presence in the deletion strain of the 5'----3' exonuclease fragment on an F' episome caused an additional 10-fold increase in spontaneous mutation frequency, resulting in mutation frequencies on the order of 50- to 100-fold greater than wild type. The mutator effect associated with the 5'----3' exonuclease gene fragment together with much of the effect attributable to the polA deletion was blocked in bacteria carrying a umuC mutation. The mutator activity therefore appears to reflect constitutive SOS induction. Excision-proficient polA deletion strains exhibited increased sensitivity to the lethal effect of UV light which was only partially ameliorated by the presence of polA+ on an F' episome. The UV-induced mutation rate to rifampin resistance was marginally lower in delta polA bacteria than in bacteria carrying the polA+ allele. This effect is unlikely to be caused by the existence of a PolI-dependent mutagenic pathway and is probably an indirect effect caused by an alteration in the pattern of excision repair, since it did not occur in excision-deficient (uvrA) bacteria. An excision-deficient polA deletion strain possessed UV sensitivity similar to that of an isogenic strain carrying polA+ on an F' episome, showing that none of the functions of PolI are needed for postreplication repair in the absence of excision repair. Our data provide no evidence for a pathway of UV mutagenesis dependent on PolI, although it remains an open question whether PolI is able to participate when it is present.

DNA Polymerase I↗
PubMed1989

Polymerases and UV mutagenesis in Escherichia coli.

Evidence for and against the involvement of the known nucleic acid polymerases in UV mutagenesis in Escherichia coli is reviewed. There is no evidence that rules out the participation of any of them when they are present but only one, the alpha subunit of DNA polymerase III holoenzyme (polC gene product) has been shown to be essential. It is argued that the PolC protein that functions in UV mutagenesis may not be immediately recognizable as one of the normal cellular polymerases or polymerase complexes.

Bacterial Proteins↗
PubMed1988

Cancer in homozygotes and heterozygotes of ataxia-telangiectasia and xeroderma pigmentosum in Britain.

We have documented mortality and cancer incidence in the families of 67 patients with ataxia-telangiectasia and 48 patients with xeroderma pigmentosum resident in Britain. For both diseases, parents of patients are obligate heterozygotes and grandparents have a probability of heterozygosity of 0.5. Fourteen ataxia-telangiectasia patients had died by June 30, 1986. This was a significant excess (14 deaths observed, 1.65 expected). Only one death was from a malignancy (non-Hodgkin's lymphoma). Three parents of ataxia-telangiectasia patients had died, all from cancer. The excess from breast cancer (two deaths observed, 0.17 expected) was statistically significant, p less than 0.05. However, no excess mortality from malignant neoplasms was found in the grandparents. Five xeroderma pigmentosum patients had died, none from internal malignancies. No excess mortality from malignant neoplasms was recorded in either their parents or grandparents.

Adolescent↗
PubMed1988

Mutagenic DNA repair in Escherichia coli. XVI. Mutagenesis by ultraviolet light plus delayed photoreversal in recA strains.

Mutagenesis was demonstrable after delayed photoreversal of UV-irradiated strains carrying a recA deletion indicating that RecA protein is not essential for the misincorporation process that is revealed by delayed photoreversal. Moreover, the data suggest that RecA protein actually depresses misincorporation to varying extents depending on the recA allele. No delayed photoreversal was demonstrable in reA1 or recA56 bacteria unless the lexA102(ind-) allele was also present. It is suggested that the level of these RecA proteins may be lower in the lexA102(ind-) strains thus minimising their depressive effect. Delayed photoreversal mutagenesis in strains carrying the recA441 allele was not affected by either adenine or guanosine plus cytidine, substances which affect the proteolytic activity of RecA441 protein.

Alleles↗
PubMed1988

Mutagenic DNA repair in Escherichia coli. XV. Mutation frequency decline of ochre suppressor mutations in umuC and lexA bacteria occurring between ultraviolet irradiation and delayed photoreversal.

Tryptophan-independent mutations were induced in CM1141 trpE65 umuC122::Tn5 following exposure to ultraviolet light (UV) plus delayed photoreversal. The mutations appeared to be exclusively class 2 ochre suppressors and showed mutation frequency decline (MFD) when the bacteria were incubated in glucose-salts medium after UV and before photoreversal. The phenomenon was similar to MFD after normal UV mutagenesis of umu+ bacteria, being inhibited in the presence of caffeine or in the absence of glucose. Mutations were also induced by UV plus delayed photoreversal in the lexA (Ind-) strain CM561, and the yield was higher than in the umuC strain suggesting that potentially mutagenic configurations might be removed or altered to some extent by the product of a gene under lexA control such that fewer were available for misincorporation events. MFD was also demonstrated in CM561 showing that this process is not dependent on the derepression of any genes under lexA control. MFD could still be demonstrated 23 min after UV at a time when most misincorporations seem to have occurred, but for technical reasons the possibility could not be excluded that the misincorporations in question could have occurred during rather than before the exposure to photoreversing light. Delayed photoreversal mutagenesis of normally non-UV-mutable strains has been interpreted as a first stage (misincorporation) of normal UV mutagenesis. The present results are consistent with this interpretation since MFD of suppressor mutations is a feature of both processes.

Bacterial Proteins↗
PubMed1987

Mutagenic DNA repair in Escherichia coli. XIV. Influence of two DNA polymerase III mutator alleles on spontaneous and UV mutagenesis.

We introduced the dnaE486 and polC74 mutations (which are associated with decreased DNA polymerase III replication fidelity) into excision defective Escherichia coli strains with varying SOS responses. These mutations increased the UV-induced frequency of base pair substitution mutations in all strains tested, except recA430 and umuC122 derivatives. This UV mutator effect therefore requires expression of the SOS error-prone repair system. In recA441 lexA51 strains where the SOS system is constitutively expressed, the UV mutator effect of the dnaE alleles was similar in relative terms (though greater in absolute terms). Since these dnaE alleles decrease rather than increase survival after UV it is argued that they promote a burst of untargeted mutations close to UV photoproducts ("hitch-hiking" mutations) rather than increase the number of translesion synthesis events. The fact that there was no UV mutagenesis in dnaE486 umuC122 or polC74 umuC122 strains indicates that infidelity associated with these dnaE alleles did not of itself enable translesion synthesis to occur. The spontaneous mutator effect conferred by dnaE486 and polC74 was not affected by umuC122 or recA430 indicating that it is not dependent upon error-prone repair ability. In recA441 lexA51 bacteria, where SOS error-prone repair is constitutively induced, the mutator effect of dnaE486 was greater and was largely blocked by umuC122. It is suggested that spontaneously occurring cryptic lesions that are themselves unable to induce the SOS system are subject to translesion synthesis under these conditions and trigger a burst of hitch-hiking mutations that are therefore effectively umuC dependent.

Alleles↗
PubMed1987

Current understanding of UV-induced base pair substitution mutation in E. coli with particular reference to the DNA polymerase III complex.

UV mutagenesis in E. coli is believed to occur in two discrete steps. The second step involves continued DNA synthesis beyond a blocking lesion in the template strand. This bypass step requires induced levels of umuD and umuC gene products and activated recA protein. DNA polymerase III may be involved since a dnaE mutator strain (believed to have defective base selection) is associated with enhanced UV mutagenesis in conjunction with a genetic background permitting the bypass step. In non-UV-mutable umu and lexA strains, UV mutagenesis can be demonstrated if delayed photoreversal is given. This is interpreted as indicating that an earlier misincorporation step can occur in such strains but the resulting mutations do not survive because the bypass step is blocked. The misincorporation step does not require any induced SOS gene products and can occur either at the replication fork or during repair replication following excision of a DNA lesion. Neither a dnaE mutator gene (leading to a defective alpha subunit of DNA polymerase III holoenzyme) nor a mutD5 mutator gene (leading to a defective epsilon proofreading subunit) had any effect on the misincorporation step. Although this is consistent with DNA polymerase III holoenzyme not being involved in the misincorporation step, other interpretations involving the inhibition of epsilon proofreading activity by recA protein are possible. In vitro studies are reported in which sites of termination of synthesis by DNA polymerase III holoenzyme on UV-irradiated M13 mp8 DNA were examined in the presence of inhibitors of the 3'-5' proofreading exonuclease (including recA protein). No evidence was found for incorporation of bases opposite photoproducts suggesting that either inhibition is more complete in the cell and/or that other factors are involved in the misincorporation step.

DNA Polymerase III↗
PubMed1987

Mutagenic DNA repair in Escherichia coli. XIII. Proofreading exonuclease of DNA polymerase III holoenzyme is not operational during UV mutagenesis.

We have introduced a mutD5 mutation (which results in defective 3'-5'-exonuclease activity of the epsilon proofreading subunit of DNA polymerase III holoenzyme) into excision-defective Escherichia coli strains with varying SOS responses to UV light. MutD5 increased the spontaneous mutation frequency in all strains tested, including recA430, umuC122::Tn5, and umuC36 derivatives. It had no effect on UV mutability or immutability in any strain or on misincorporation revealed by delayed photoreversal in UV-irradiated umuC36, umuC122::Tn5, or recA430 bacteria. It is concluded that the epsilon proofreading subunit of DNA polymerase III holoenzyme is excluded, inhibited, or inoperative during misincorporation and mutagenesis after UV.

Arginine↗
PubMed1987

Specificity of mutation by UV light and delayed photoreversal in umuC-defective Escherichia coli K-12: a targeting intermediate at pyrimidine dimers.

Prototrophic mutants produced by UV light in Escherichia coli K-12 strains with argE3(Oc) and hisG4(Oc) defects are distinguished as backmutations and specific nonsense suppressor mutations. In strains carrying a umuC defect, mutants are not produced unless irradiated cells are incubated and then exposed to photoreversing light (delayed photoreversal mutagenesis). The mutants thus produced are found to be specifically suppressor mutations and not backmutations. The suppressor mutations are primarily glutamine tRNA ochre suppressor mutations, which have been attributed previously to mutation targeted at T = C pyrimidine dimers. In a lexA51 recA441 strain, where the SOS mutagenesis functions are constitutive, targeting at dimers is confirmed by demonstrating that the induction of glutamine tRNA suppressor mutations is susceptible to photoreversal. In the same strain induction of backmutations is not susceptible to photoreversal. Thus delayed photoreversal mutagenesis produces suppressor mutations that can be targeted at pyrimidine dimers and does not produce backmutations that are not targeted at pyrimidine dimers. This correlation supports the idea that delayed photoreversal mutagenesis in umuC defective cells reflects a mutation process arrested at a targeting pyrimidine dimer photoproduct, which is the immediate cause of both the alteration in DNA sequence and the obstruction (unless repaired) to mutation fixation and ultimate expression.

Arginine↗