DNA-damaging activity of patulin in Escherichia coli

At a concentration of 10 micrograms/ml, patulin caused single-strand DNA breaks in living cells of Escherichia coli. At 50 micrograms/ml, double-strand breaks were observed also. Single-strand breaks were repaired in the presence of 10 micrograms of patulin per ml within 90 min when the cells were incubated at 37 degrees C in M9-salts solution without a carbon source. The same concentration also induced temperature-sensitive lambda prophage and a prophage of Bacillus megaterium. When an in vitro system with permeabilized Escherichia coli cells was used, patulin at 10 micrograms/ml induced DNA repair synthesis and inhibited DNA replication. The in vivo occurrence of DNA strand breaks and DNA repair correlated with the in vitro induction of repair synthesis. In vitro the RNA synthesis was less affected, and overall protein synthesis was not inhibited at 10 micrograms/ml. Only at higher concentrations (250 to 500 micrograms/ml) was inhibition of in vitro protein synthesis observed. Thus, patulin must be regarded as a mycotoxin with selective DNA-damaging activity.     

DNA-damaging activity of patulin in Escherichia coli.

At a concentration of 10 micrograms/ml, patulin caused single-strand DNA breaks in living cells of Escherichia coli. At 50 micrograms/ml, double-strand breaks were observed also. Single-strand breaks were repaired in the presence of 10 micrograms of patulin per ml within 90 min when the cells were incubated at 37 degrees C in M9-salts solution without a carbon source. The same concentration also induced temperature-sensitive lambda prophage and a prophage of Bacillus megaterium. When an in vitro system with permeabilized Escherichia coli cells was used, patulin at 10 micrograms/ml induced DNA repair synthesis and inhibited DNA replication. The in vivo occurrence of DNA strand breaks and DNA repair correlated with the in vitro induction of repair synthesis. In vitro the RNA synthesis was less affected, and overall protein synthesis was not inhibited at 10 micrograms/ml. Only at higher concentrations (250 to 500 micrograms/ml) was inhibition of in vitro protein synthesis observed. Thus, patulin must be regarded as a mycotoxin with selective DNA-damaging activity.     

Role of protein synthesis in the survival of carbon-starved Escherichia coli K-12.

In a typical Escherichia coli K-12 culture starved for glucose, 50% of the cells lose viability in ca. 6 days (Reeve et al., J. Bacteriol. 157:758-763, 1984). Inhibition of protein synthesis by chloramphenicol resulted in a more rapid loss of viability in glucose-starved E. coli K-12 cultures. The more chloramphenicol added (i.e., the more protein synthesis was inhibited) and the earlier during starvation it was added, the greater was its effect on culture viability. Chloramphenicol was found to have the same effect on a relA strain as on an isogenic relA+ strain of E. coli. Addition of the amino acid analogs S-2-aminoethylcysteine, 7-azatryptophan, and p-fluorophenylalanine to carbon-starved cultures to induce synthesis of abnormal proteins had an effect on viability similar to that observed when 50 micrograms of chloramphenicol per ml was added at zero time for starvation. Both chloramphenicol and the amino acid analogs had delayed effects on viability, compared with their effects on synthesis of normal proteins. The need for protein synthesis did not arise from cryptic growth, since no cryptic growth of the starving cells was observed under the conditions used. From these and previous results obtained from work with peptidase-deficient mutants of E. coli K-12 and Salmonella typhimurium LT2 (Reeve et al., J. Bacteriol. 157:758-763, 1984), we concluded that a number of survival-related proteins are synthesized by E. coli K-12 cells as a response to carbon starvation. These proteins are largely synthesized during the early hours of starvation, but their continued activity is required for long-term survival.     

The influence of chloramphenicol on synthesis of ribosomes and beta and beta' subunits of RNA polymerase]

The effect of low chloramphenicol concentrations on the biosynthesis of RNA, ribosomal proteins and RNA polymerase in E. coli CP 78 cells was studied. When protein synthesis was decreased by 50--70%, 14C-uracil incorporation in DNA increased twice, the rRNA synthesis being stimulated preferentially. In the presence of antibiotic the RNA/DNA ratio increased from 5,7 to 13,3. The differential rate of r-protein synthesis increased simultaneously with the stimulation of rRNA synthesis, so that alphar rises from 0,083 (without antibiotic) to 0,122 and 0,161 at 5 and 10 microgram/ml of chloramphenicol, respectively. The inhibition of protein synthesis by chloramphenicol is accompanied also by the increase of differential rate of synthesis of beta and beta' subunits of RNA polymerase. In the presence of 5 and 10 microgram/ml of chloramphenicol, alphap increased from 0,90% to 1,44 and 1,57%, respectively. It is assumed that the genes for beta and beta' subunits of RNA polymerase as the ribosomal genes are negatively controlled by guanosine tetraphosphate which intracellular concentration decreased in the presence of chloramphenicol. The known data on the influence of streptolydigin and rifampicin on the RNA polymerase biosynthesis are discussed in view of proposed hypothesis.     

Mechanism of thermoresistance in Escherichia coli cells exposed to temperature elevation

The influence of media with different osmotic pressure (NaCl water solution) and chloramphenicol (10 micrograms/ml) on the survival, permeability, and survival curve shape of Escherichia coli B/r and E. coli Bs-1 cells, heated up to 50, 52, and 60 degrees C was investigated. As shown, the survival curve of cells heated up to 60 degrees C in isotonic conditions was characterized by exponential shape, while the survival curves of cells heated up to 50 and 52 degrees C consisted of two components characterizing thermosensitive and thermoresistant parts of cell population. Hypertonic conditions of heat at 52 degrees C decreased cell lethality and permeability. In this case, survival curves were characterized by exponential shape. Chloramphenicol was shown to protect against damaging action of heat at 50 degrees C and not to affect the viability of cells heated at 52 and 60 degrees C. It is proposed that the increase of cell thermoresistance with heat dose elevation at 50 and 52 degrees C in isotonic conditions, which is accompanied by the appearance of thermotolerant components on survival curves, may be associated with accommodational cell reactions. The essence of these reactions consists in stabilization of the osmotic cell homeostasis.     

Low-temperature conditional cell division mutants of Escherichia coli.

Fifteen low-temperature conditional division mutants of Escherichia coli K-12 was isolated. They grew normally at 39 degrees C but formed filaments at 30 degrees C. All exhibited a coordinated burst of cell division when the filaments were shifted to the permissive temperature (39 degrees C). None of the various agents that stimulate cell division in other mutant systems (salt, sucrose, ethanol, and chloramphenicol) was very effective in restoring colony-forming ability at 25 degrees C or in stimulating cell division in broth. One of these mutants, strain JS10, was found to have an altered cell envelope as evidenced by increased sensitivity to deoxycholate and antibiotics, as well as leakage of ribonulcease I, a periplasmic enzyme. This mutant had normal rates of DNA synthesis, RNA synthesis, and phospholipid synthesis at both the nonpermissive and permissive temperatures. However, strain JS10 required new protein synthesis in the apparent absence of new RNA synthesis for division of filaments at the permissive temperature. The division of lesion in strain JS10 is cotransducible with malA, aroB, and glpD and maps within min 72 to 75 on the E. coli chromosome.     

Cell-to-cell adhesion of dissociated embryonic brain cells; the effects of metabolic inhibitors and temperature

Brain cells from 16 to 18-day-old mice embryos were dissociated by mild trypsinization and rotated for 120 min. The area and density of of the adhesive complexes formed were registered using the method described previously. The adhesiveness of dissociated embryonic brain cells (measured during the 120 min of rotation) was diminished in the presence of inhibitors of protein synthesis (puromycin, cycloheximide and inhibition of mRNA synthesis actinomycin D). The inhibition was, however, not distinct, because 1 microgram/ml of cycloheximide and actinomycin was without any significant effect, and the degree of inhibition evoked by 10 micrograms/ml and 25 micrograms/ml of puromycin bordered on significance. However, protein synthesis inhibitors in long-term aggregation experiments had a pronounced inhibitory effect and/or induced destruction of the aggregates. Metabolic inhibitors (KCN and NaN3) caused an inhibition at the lowest level of significance (p less than 0.05) 10(-3) mol/l KCN reduced the final adhesive product significantly. Cells rotated at room temperature and at +5 degrees C adhere to the same extent as in control experiments (37 degrees C). The adhesion was significantly inhibited at +60 degrees C and also after freezing at -80 degrees C with subsequent thawing. The adhesion of cells exposed for 30 min to between +80 degrees C and 100 degrees C was completely abolished. The process of embryonic brain cell adhesion requires a low energy supply, and is relatively independent of biosynthetic processes and of temperature changes between +5 degrees C and +50 degrees C.     

CspA, CspB, and CspG, major cold shock proteins of Escherichia coli, are induced at low temperature under conditions that completely block protein synthesis

CspA, CspB, and CspG, the major cold shock proteins of Escherichia coli, are dramatically induced upon temperature downshift. In this report, we examined the effects of kanamycin and chloramphenicol, inhibitors of protein synthesis, on cold shock inducibility of these proteins. Cell growth was completely blocked at 37 degrees C in the presence of kanamycin (100 microgram/ml) or chloramphenicol (200 microgram/ml). After 10 min of incubation with the antibiotics at 37 degrees C, cells were cold shocked at 15 degrees C and labeled with [35S]methionine at 30 min after the cold shock. Surprisingly, the synthesis of all these cold shock proteins was induced at a significantly high level virtually in the absence of synthesis of any other protein, indicating that the cold shock proteins are able to bypass the inhibitory effect of the antibiotics. Possible bypass mechanisms are discussed. The levels of cspA and cspB mRNAs for the first hour at 15 degrees C were hardly affected in the absence of new protein synthesis caused either by antibiotics or by amino acid starvation.     

Lack of complete cooperativity of ribosome assembly in vitro and its possible relevance to in vivo ribosome assembly and the regulation of ribosomal gene expression.

Earlier studies have shown that the reconstitution of Escherichia coli 50S as well as 30S ribosomal subunits from component rRNA and ribosomal protein (r-protein) molecules in vitro is not completely cooperative and binding of more than one r-protein to a single 16S rRNA (or 23S rRNA) molecule is required to initiate a successful 30S (or 50S) ribosome assembly reaction. We first confirmed this conclusion by carrying out 30S subunit reconstitution in the presence of a constant amount of 16S rRNA together with various amounts of total 30S r-proteins (TP30) and by analyzing the physical state of reconstituted particles rather than by assaying protein synthesizing activity of the particles as was done in the earlier studies. As expected, under conditions of excess rRNA, the efficiency of 30S subunit reconstitution per unit amount of TP30 decreased greatly with the decrease in the ratio of TP30 to rRNA, indicating the lack of complete cooperativity in the assembly reaction. We then asked the question whether the cooperativity of ribosome assembly is complete in vivo. We treated exponentially growing E coli cells with low concentrations of chloramphenicol which is known to inhibit protein synthesis without inhibiting rRNA synthesis, creating conditions of excess synthesis of rRNA relative to r-proteins. Several concentrations of chloramphenicol (ranging from 0.4 to 4.0 micrograms/ml) were used so that inhibition of protein synthesis ranged from 40 to 95%. Under these conditions, we examined the synthesis of RNA, ribosomal proteins and 50S ribosomal subunits as well as the synthesis of total protein. We found that the synthesis of 50S subunits was not inhibited as much as the synthesis of total protein at lower concentrations of chloramphenicol, but the degree of inhibition of 50S subunit synthesis increased sharply with increasing concentrations of chloramphenicol and was in fact greater than the degree of inhibition of total protein synthesis at chloramphenicol concentrations of 2 micrograms/ml or higher. The inhibition of 50S subunit synthesis was significantly greater than the inhibition of r-protein synthesis at all chloramphenicol concentrations examined. These data are consistent with the hypothesis that the cooperativity of ribosome assembly in vivo is also not complete as is the case for in vitro ribosome reconstitution, but are difficult, if not impossible, to explain on the basis of the complete cooperativity model.(ABSTRACT TRUNCATED AT 400 WORDS)     

The Characteristics and Genetic Map Location of a Temperature Sensitive DNA Mutant of E. COLI K12

A temperature sensitive strain of E. coli K12 has been isolated in which residual DNA synthesis occurs at the 40 degrees C restrictive temperature; syntheses of RNA, protein and DNA precursors are not directly affected. The mutation has been designated dna-325 and is located at 89 min on the E. coli map in the same region where the dnaC locus is found. dnaC mutants are considered to be defective in DNA initiation. Some of the data are consistent with the view that the dna-325 mutation is temperature sensitive in the process of DNA initiation rather than DNA chain elongation: (1) more than two cell divisions occur after a shift to 40 degrees C; (2) upon a shift down to 30 degrees C, cell division occurs again only after the DNA content of the cells has doubled; (3) 80% more DNA is made at 30 degrees C in the presence of chloramphenicol after prior inhibition of DNA synthesis at 40 degrees C. These three observations indicate that rounds of DNA replication were completed at 40 degrees C. Also (4) infective lambda particles can be made at 40 degrees C long after bacterial DNA replication has ceased. It appears however that some DNA initiation can occur at 40 degrees C since (1) a limited amount of DNA synthesis does occur at 40 degrees C after prior alignment of the chromosomes by amino acid starvation at 30 degrees C, and (2) after incubation in bromouracil at the restrictive temperature, heavy DNA is found with both strands containing bromouracil.     

Effects of rifampicin, streptolydigin and actinomycin D on the replication of Col E1 plasmid DNA in Escherichia coli

We recently reported (Clewell et al., 1972) on an inhibitory effect of rifampicin on Col E1 plasmid replication. The present study represents a further characterization of this phenomenon as well as a study of the effects of two other known inhibitors of RNA synthesis, Streptolydigin and actinomycin D.During treatment of cells with chloramphenicol the colicinogenic factor E₁ (Col E1) continues to replicate for more than ton hours. During this time 4 to 5 S RNA is also synthesized. When varying concentrations of rifampicin were included during chloramphenicol treatment, inhibition of plasmid DNA synthesis correlated very closely with inhibition of cellular RNA synthesis. Similar experiments testing the effects of Streptolydigin and actinomycin D (during chloramphenicol treatment) showed that cellular RNA synthesis was at least 100 times more sensitive to these drugs than was plasmid DNA synthesis.When actively growing cells (i.e. cells not treated with chloramphenicol) were treated with a high concentration of rifampicin (250 μg/ml), chromosomal DNA synthesis continued to an extent representing about a 50% increase in DNA, while plasmid DNA synthesis appeared to stop abruptly.     

Replication of G4 progeny double-stranded DNA in dna mutants of Escherichia coli.

Host functions required for replication of progeny double-stranded DNA of bacteriophage G4 were examined by using metabolic inhibitors and Escherichia coli dna mutants. In dna+ bacteria, synthesis of the progeny replicative form (RF) was relatively resistant to 30 microgram/ml of chloramphenicol, but considerably sensitive to 200 microgram/ml of rifampicin. The RF replication was severely inhibited by 50 microgram/ml of mitomycin C, 50 microgram/ml of nalidixic acid, or 200 microgram/ml of novobiocin. At 41 degrees C, synthesis of G4 progeny RF was distinctly affected in a dnaC(D) mutant and in a dnaG host. The progeny RF replication was prevented at 42 degrees C in a dnaE strain as well as in a dnaB mutant. In a dnaZ strain, the synthetic rate of the progeny RF was markedly reduced at 42 degrees C. At 43 degrees C, the rate of G4 progeny RF synthesis was reduced even in dna+ or dnaA bacteria, but significant amounts of the progeny RF were still synthesized in these hosts at the high temperature. In addition to five dna gene products, host rep function was essential for the RF replication.     

Effect of tunicamycin on glycosylation of a 50 kDa protein and thermotolerance development.

We investigated whether or not a 50 kDa glycoprotein might play an important role in protein synthesis-independent thermotolerance development in CHO cells. When cells were heated for 10 min at 45.5 degrees C, they became thermotolerant to a heat treatment at 45.5 degrees C administered 12 hr later. The thermotolerance ratio at 10(-3) isosurvival was 4.4. The cellular heat shock response leads to enhanced glycosylation of a 50 kDa protein. The glycosylation of proteins including a 50 kDa glycoprotein was inhibited by treatment with various concentrations of tunicamycin (0.2-2 micrograms/ml). The development of thermotolerance was not affected by treatment with tunicamycin after the initial heat treatment, although 2 micrograms/ml tunicamycin inhibited glycosylation by 95%. However, inhibiting protein synthesis with cycloheximide (10 micrograms/ml) after the initial heat treatment partially inhibited the development of thermotolerance. Nevertheless, there was no further reduction of thermotolerance development by treatment with a combination of 2 micrograms/ml tunicamycin and 10 micrograms/ml cycloheximide. These data suggest that development of thermotolerance, especially protein synthesis-independent thermotolerance, is not correlated with increased glycosylation of the 50 kDa protein.     

Nuclear protein synthesis in a temperature-sensitive Chinese hamster ovary cell line at 40 degrees C

We examined the incorporation of radioactive amino acids into nuclear proteins occurring at nonpermissive conditions in tsH1 Chinese hamster ovary cells with a temperature-sensitive defect in cytosol nonmitochondrial protein synthesis. In leucine-free medium at 40 degrees C, total cellular protein synthesis declined by 1-1.5%/min. As reported by others, preincubating these cells at 42 degrees C for 5-10 min sharply increased the rate of decline. The synthesis of acidic nuclear proteins at nonpermissive conditions (40 degrees C + 300 micrograms/ml cycloheximide) was demonstrated by the nuclear incorporation of 3H-tryptophan. Radioactivity, seen by autoradiography to be associated with these isolated Triton-X-100-washed nuclei, was released after incubating labelled nuclei with proteolytic enzymes. During incubation of tsH1 cells at nonpermissive conditions, pulse/chase experiments were consistent with the loss of some nuclear radioactivity into the cytoplasm. The distribution of cytosol and nuclear proteins, labelled at permissive or nonpermissive conditions and separated by isoelectric focusing, differed quantitatively and probably qualitatively, confirming the residual synthesis of acidic nuclear proteins at 40 degrees C in the presence of cycloheximide. Most newly synthesized acidic proteins retained by nuclei from cells labeled at nonpermissive conditions were present in a transciptionally active chromatin fraction. Although under these conditions the apparent rate of cellular RNA synthesis was unchanged, inhibiting residual cycloheximide-resistant nuclear protein synthesis with puromycin proportionately reduced RNA synthesis. Preincubating cells with 20 micrograms/ml of actinomycin D did not inhibit residual labelling of nuclear proteins; effects on residual nuclear labelling of impaired mitochondrial respiration were ambiguous. Nuclear proteins labelled under nonpermissive conditions probably included some of the 'prompt' heat shock proteins recently described. Provided certain assumptions are correct, our results are consistent with very limited protein synthesis associated with and even intrinsic to cell nuclei. They also suggest that this residual cycloheximide-resistant protein synthesis could be concerned with optimum synthesis or processing of certain nuclear RNA species.     

The mechanism of action of DuP 721, a new antibacterial agent: effects on macromolecular synthesis

Pulse labeling studies with Bacillus subtilis showed that DuP 721 inhibited protein synthesis. The IC50 of DuP 721 for protein synthesis was 0.25 micrograms/ml but it was greater than 32 micrograms/ml for RNA and DNA synthesis. In cell-free systems, DuP 721 concentrations up to 100 microM did not inhibit peptide chain elongation reactions under conditions where chloramphenicol, tetracycline and hygromycin B inhibited these reactions. Furthermore, Dup 721 did not cause phenotypic suppression of nonsense mutations suggesting that DuP 721 did not inhibit peptide chain termination. Thus, the mechanism of action of DuP 721 is at a target preceeding chain elongation.     

Cassia alata and the preclinical search for therapeutic agents for the treatment of opportunistic infections in AIDS patients.

In our search for therapeutic agents from natural sources with potential for the treatment of opportunistic infections in patients afflicted with acquired immunodeficiency syndrome (AIDS), we investigated antibacterial and antifungal activities of water extracts of Cassia alata (C. alata). The extracts are traditionally used in Ivory Coast, West Africa to treat bacterial infections caused by Escherichia coli (E. coli), and fungal infections caused by Candida albicans (C. albicans) and dermatophytes. Our working hypothesis was that the extract contains active ingredient(s) which can be isolated, identified and developed into useful antibacterial/antifungal agents for the treatment of opportunistic infections in patients with AIDS. We used the broth dilution and agar dilution methods. Specifically, we focused on E. coli and C. albicans and the effectiveness of the extracts was evaluated relative to those of standard antibacterial agent chloramphenicol and antifungal agent amphotericin B. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for the water extract of C. alata against E. coli were 1.6 mg/ml and 60 mg/ml, respectively; corresponding data for chloramphenicol were 2 micrograms/ml and 10 micrograms/ml. Similarly, the MIC and minimum fungicidal concentration (MFC) for the extract against C. albicans were 0.39 mg/ml and 60 mg/ml in contrast to 0.58 micrograms/ml and 0.98 micrograms/ml for amphotericin B. From the dose-response curve plots, the extract had an IC50 of 31 mg/ml for E. coli and 28 mg/ml for C. albicans. The data suggest that C. alata extracts contain agent(s) which have therapeutic potential and might be useful if isolated and developed for the treatment of opportunistic infections of AIDS patients.     

Cell death in Escherichia coli dnaE(Ts) mutants incubated at a nonpermissive temperature is prevented by mutation in the cydA gene

Cells of the Escherichia coli dnaE(Ts) dnaE74 and dnaE486 mutants die after 4 h of incubation at 40 degrees C in Luria-Bertani medium. Cell death is preceded by elongation, is inhibited by chloramphenicol, tetracycline, or rifampin, and is dependent on cell density. Cells survive at 40 degrees C when they are incubated at a high population density or at a low density in conditioned medium, but they die when the medium is supplemented with glucose and amino acids. Deletion of recA or sulA has no effect. We isolated suppressors which survived for long periods at 40 degrees C but did not form colonies. The suppressors protected against hydroxyurea-induced killing. Sequence and complementation analysis indicated that suppression was due to mutation in the cydA gene. The DNA content of dnaE mutants increased about eightfold in 4 h at 40 degrees C, as did the DNA content of the suppressed strains. The amount of plasmid pBR322 in a dnaE74 strain increased about fourfold, as measured on gels, and the electrophoretic pattern appeared to be normal even though the viability of the parent cells decreased 2 logs. Transformation activity also increased. 4',6'-diamidino-2-phenylindole staining demonstrated that there were nucleoids distributed throughout the dnaE filaments formed at 40 degrees C, indicating that there was segregation of the newly formed DNA. We concluded that the DNA synthesized was physiologically competent, particularly since the number of viable cells of the suppressed strain increased during the first few hours of incubation. These observations support the view that E. coli senses the rate of DNA synthesis and inhibits septation when the rate of DNA synthesis falls below a critical level relative to the level of RNA and protein synthesis.     

Characterization of the effect of aphidicolin on adenovirus DNA replication: evidence in support of a protein primer model of initiation

Adenovirus DNA replication is inhibited by aphidicolin but the inhibition clearly has different parameters than the inhibition of purified DNA polymerase alpha. In adenovirus infected Hela cells, 10 micrograms/ml of aphidicolin reduced viral DNA synthesis by 80%. Cellular DNA synthesis was inhibited by 97% at 0.1 microgram/ml. 10 micrograms/ml of drug had no effect on virus yield or late protein synthesis though higher concentrations of drug (50 micrograms/ml) caused an abrupt cessation of late protein synthesis and 100 micrograms/ml reduced virus yield by 3 logs. Concentrations of the drug from 0.5 microgram/ml to 10 micrograms/ml were found to dramatically slow the rate of DNA chain elongation in vitro but not stop it completely, so that over a long period of time net incorporation was reduced only slightly compared to the control. 50 micrograms/ml or 100 micrograms/ml of drug completely inhibited incorporation in vitro. Initiation of viral DNA replication - covalent attachment of dCMP to the preterminal protein - occurs in vitro. This reaction was found to be insensitive to inhibition by aphidicolin. We thus conclude that aphidicolin exerts its effect on adenovirus DNA chain elongation, but not on the primary initiation event of protein priming.