Biomedical subjects

P L Foster

Publications and source records attributed to P L Foster.

48 records · Page 3Linked to original sources

PubMed1989

Presence of the dnaQ-rnh divergent transcriptional unit on a multicopy plasmid inhibits induced mutagenesis in Escherichia coli.

In Escherichia coli the dnaQ+ gene, which encodes epsilon, a fidelity subunit of DNA polymerase III, and the rnh+ gene, which encodes RNase H, share a promoter region but are transcribed in opposite directions. The presence of this divergent transcriptional unit on a multicopy plasmid inhibited by as much as 10-fold mutations induced by the SOS-dependent mutagens methyl methanesulfonate and UV light. Mutations in either gene eliminated the effect, suggesting that both genes contribute either directly or indirectly to the antimutagenic phenotype. Neither survival to mutagen exposure nor induction of the SOS response was comparably affected by the presence of the genes. Although the antimutagenic phenotype was partially suppressed by excess UmuDC proteins, which are required for SOS mutagenesis, the presence of the dnaQ+-rnh+ clone also reduced the induction of mutations by N-methyl-N'-nitro-N-nitrosoguanidine in cells deficient for SOS mutagenic processing. The results suggest that the presence of the dnaQ+-rnh+ divergent transcriptional unit interferes with an underlying mutagenic mechanism that is normally facilitated by the proteins induced as part of the SOS response.

Blotting, Western↗

PubMed1988

Interactions between epsilon, the proofreading subunit of DNA polymerase III, and proteins involved in the SOS response of Escherichia coli.

Epsilon, a fidelity subunit of Escherichia coli DNA Polymerase III, is encoded by dnaQ+. dnaQ49 is a recessive allele that confers temperature-sensitive and salt-suppressible phenotypes for both replication fidelity and viability. SOS mutagenesis in E. coli is regulated by LexA and requires activated RecA (RecA*) and the products of the umuDC operon. dnaQ49 strains with various recA, lexA and umuDC alleles were constructed to determine if activities induced as part of the SOS response influence epsilon activity. We found: (1) both UmuDC and RecA* independently enhance the dnaQ49 mutator phenotype, and (2) expression of RecA* activity in the absence of UmuDC function increases the temperature sensitivity for viability of dnaQ49. These results support the hypothesis that RecA and one or both of the UmuDC proteins interact with the replication complex during SOS mutagenesis.

Alleles↗

PubMed1988

Cartilage sulfation inhibitor from rat liver: partial characterization of properties and biologic action.

Cartilage sulfation (somatomedin) inhibitors (CSI) from rat liver produce reversible inhibition of cartilage growth. After gel filtration Sephadex G-200, CSI appear to have MW approximately 100,000 and they are urea- and trypsin-labile factors. To explore further the mechanism of CSI action, we used the chick pelvic rudiment bioassay and studied the effect of CSI on the incorporation on 35S-sulfate (proteoglycan synthesis), 14C-leucine (protein synthesis), 3H-uridine (RNA synthesis), and 3H-thymidine (DNA synthesis). Normal rat serum (NRS) significantly stimulated the incorporation of all four isotopes, as expected. After a 24-hour incubation, CSI significantly blunted cartilage stimulation by NRS regarding total isotope uptake (1), 35S-sulfate (NRS, 96 +/- 8 mcg/100 mg cartilage dry weight; NRS + CSI, 48 +/- 4, mean +/- SEM, n = 29, P less than .05); and (2) 14C-leucine (NRS, 2,089 +/- 172 cpm/mg dry weight; NRS + CSI, 1,102 +/- 141, n = 18, P less than .05); and (3) 3H-uridine (NRS, 6,711 +/- 832 cpm/mg; NRS + CSI, 3,227 +/- 425 cpm/mg, n = 18, P less than .05); but not (4) 3H-thymidine (NRS, 3,540 +/- 620 cpm/mg; NRS + CSI 3,249 +/- 285, n = 19). The inhibition of 35S-sulfate and 14C-leucine uptake by CSI was dose-dependent and reversible. For 35S-sulfate, uptake by cartilage incubated with CSI alone for 40 hours was 13 +/- 3 micrograms/100 mg; with CSI for 16 hours then fresh medium with NRS for 24 hours uptake was 39 +/- 12, P less than .05.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

An analysis of the mutagenicity of 1,2-dibromoethane to Escherichia coli: influence of DNA repair activities and metabolic pathways.

The mutagenicity of 1,2-dibromoethane (EDB) to Escherichia coli was reduced by the UV light-induced excision repair system but unaffected by the loss of a major apurinic/apyrimidinic site repair function. At high doses, 70-90% of the EDB-induced mutations were independent of SOS-mutagenic processing and approximately 50% were independent of glutathione conjugation. The SOS-independent mutations induced by EDB were unaffected by the enzymes that repair alkylation-induced DNA lesions. EDB-induced base substitutions were dominated by GC to AT and AT to GC transitions. These results suggest that EDB-induced premutagenic lesions have some, but not all, of the characteristics of simple alkyl lesions.

Biotransformation↗

PubMed1988

Induction of base substitution mutations by aflatoxin B1 is mucAB dependent in Escherichia coli.

Recovery of aflatoxin B1-induced base substitution mutations in Escherichia coli was almost completely dependent on the presence of the SOS-mutagenesis-enhancing operon mucAB+; the normal E. coli analog, umuDC+, was not sufficient. Yet aflatoxin B1 induced the SOS response, including the umuDC operon, as well as did UV light. Neither preinduction of the SOS response nor the presence of additional copies of umuDC+ allowed the recovery of aflatoxin B1-induced base substitutions. Thus, the premutagenic DNA lesions induced by aflatoxin B1 reveal a functional difference between UmuDC and MucAB. We estimate that in the presence of MucAB the probability that aflatoxin B1-induced DNA lesions will be converted into mutations is increased at least 10-fold.

Aflatoxin B1↗

PubMed1987

Alcoholic women.

Explore the source record for details and available documents.

Alcoholism↗

PubMed1987

Loss of an apurinic/apyrimidinic site endonuclease increases the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine to Escherichia coli.

xthA- Escherichia coli, which are missing a major cellular apurinic/apyrimidinic (AP) endonuclease, are 5- to 10-fold more sensitive than xthA+ bacteria to mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) under conditions that induce the "adaptive response." The xthA(-)-dependent mutations are also dependent on SOS mutagenic processing and consist of both transversion and transition base substitutions. When MNNG-adapted xthA- bacteria are challenged with a high dose of MNNG, more xthA(-)-dependent SOS-dependent mutations are induced, and transversions are enhanced relative to transitions. The mutations induced by challenge are eliminated in xthA- alkA- bacteria, which are also deficient for 3-methyladenine glycosylase II activity. These data are consistent with the hypothesis that AP sites, at least some of which are produced by glycosylase activity, are mutagenic intermediates following cellular DNA alkylation.

Codon↗

PubMed1987

Creation of a test plasmid for detecting G-C-to-T-A transversions by changing serine to arginine in the active site of beta-lactamase.

Oligonucleotide-directed mutagenesis of the beta-lactamase gene, bla, on pBR322 was used to change the codon for the active-site serine 70, AGC, to CGC, coding for arginine. Escherichia coli cells carrying the mutant plasmid, pGD104, were sensitive to ampicillin, indicating that the arginine-containing enzyme is inactive. We characterized the reversion of the mutant bla gene by a number of mutagens and in different genetic backgrounds and demonstrated that full ampicillin resistance can be restored only by a G-C-to-T-A transversion occurring at the first base of the codon. Thus, reversion of the mutant bla gene is diagnostic for G-C-to-T-A transversions, and bacteria carrying pGD104 can be used as test strains to detect the occurrence of this mutation.

Aflatoxins↗

PubMed1985

Induction of transversion mutations in Escherichia coli by N-methyl-N'-nitro-N-nitrosoguanidine is SOS dependent.

Escherichia coli alkA mutants, which are deficient for an inducible DNA glycosylase, 3-methyladenine-DNA glycosylase II, are sensitive to mutagenesis by low doses of the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). As many as 90% of the alkA-dependent mutations induced by MNNG are also umuC+ dependent and thus are due to DNA lesions that are substrates for the mutagenic functions of the SOS response. A great number of these mutations are base substitutions at A . T sites, particularly A . T transversions. We discuss which DNA lesions may be responsible for these mutations. Our results show that the induction of 3-methyladenine-DNA glycosylase II, which occurs as part of the adaptive response to alkylating agents such as MNNG, significantly reduces the mutagenicity as well as the lethality of alkylation damage.

Alkylation↗

PubMed1983

Base substitution mutations induced by metabolically activated aflatoxin B1.

We have determined the base substitutions generated by metabolically activated aflatoxin B1 in the lacI gene of a uvrB- strain of Escherichia coli. By monitoring over 70 different nonsense mutation sites, we show that activated aflatoxin B1 specifically induced GxC leads to TxA transversions. One possible pathway leading to this base change involves depurination at guanine residues. We consider this mechanism of mutagenesis in the light of our other findings that the carcinogens benzo[a]pyrene diol epoxide and N-acetoxyacetylaminofluorene also specifically induce GxC leads to TxA transversions.

Aflatoxin B1↗

PubMed1983

Distribution and specificity of mutations induced by neocarzinostatin in the lacI gene of Escherichia coli.

Although neocarzinostatin (NCS) attacks DNA almost exclusively at adenine and thymine residues in vitro, exposure of Escherichia coli to this antitumor drug resulted in a high frequency of mutations at guanine:cytosine base pairs in the lacI gene. Thus, NCS-induced base substitution mutations do not appear to result from the major DNA lesions that have been biochemically characterized. The overall distribution of nonsense mutations produced by NCS was distinctly nonrandom, consisting in part of a few "hotspots" and a large number of "coldspots." The existence of these coldspots implies that untargeted mutagenesis does not make a significant contribution to the mutations induced by this SOS-dependent mutagen.

Antibiotics, Antineoplastic↗

PubMed1982

Random components in mutagenesis.

The mutability of DNA varies enormously from one base pair to another. Part of this variation is due to the specificity of the reaction between mutagens and base, but much of the variation is due to unknown causes. A genetic system developed by Miller and colleagues allows the mutation frequencies of a large number of different base pairs in the lacI gene of Escherichia coli to be compared. For example, Coulondre and Miller found that the sites most readily mutated by UV light are almost 100 times more often mutated than the least susceptible sites. A recently completed study of mutagenesis with neocarzinostatin (NCS) in the lacI gene has prompted us to re-examine some previous studies, of mutagenesis in this gene. Our analysis, reported here, suggests that the mutations induced by certain mutagens fall into two classes: mutations in one class are clearly distributed non-randomly, that is, they are very common at some sites and significantly less common at others; mutations in the second class, however, occur at low frequency and appear to be randomly distributed. Both classes of mutations seem to occur only at damaged bases.

4-Nitroquinoline-1-oxide↗