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F Masek

Publications and source records attributed to F Masek.

At least 19 recordsLinked to original sources
PubMed2000

Inducible stable DNA replication (iSDR) and the uvr-dependent tolerance of pyrimidine dimers in UV-irradiated Escherichia coli are two uncoupled processes.

Inducible stable DNA replication (iSDR) is dependent on recombination and is supposed to play a role in DNA repair of Escherichia coli. Our previous data suggested that iSDR may be involved in the tolerance of UV lesions, which remain unexcised in excision-proficient E. coli exposed to some UV pretreatments. Now, the tolerance of unexcised lesions has been followed in E. coli recB21 and in E. coli priA1 sup mutants, incapable of iSDR. The obtained data do not confirm the previous hypothesis about the involvement of iSDR in the putative uvr-dependent lesion tolerance. They rather suggest that iSDR and the uvr-dependent lesion tolerance are two uncoupled processes.

DNA Repair↗
PubMed1997

The pre-UV nutritional stresses increase UV resistance, decrease UV mutagenesis and inhibit excision repair.

Nutritional stresses applied to E. coli prior to UV irradiation increase UV resistance and decrease UV mutagenesis. This effect is uvrA-dependent and might reflect a more efficient excision of pyrimidine dimers [1]. The data presented here, however, indicate that after prestarvation for glucose or amino acids pyrimidine dimer excision (PDE) was partly inhibited. It appears that the stress conditions stimulate a mode of uvr-dependent tolerance of lesions, efficient and precise. Possible modes of PDE inhibition and lesion tolerance are discussed.

Adenosine Triphosphatases↗
PubMed1997

The effect of the OmpT protease on excision repair in UV-irradiated Escherichia coli.

The extent of pyrimidine dimer excision (PDE) was inhibited in UV-irradiated E. coli KS272 (ompT+) cells when they were preinduced by a low UV predose preceded by a nutrition stress but not in the preinduced E.coli SF100 (ompT-) mutants. The preinduction, however, markedly inhibited PDE in the ompT- cells transformed with a multicopy plasmid carrying ompT gene. The data are consistent with the hypothesis that the inducible OmpT protease (controlled by rpoH) might terminate the SOS period of excision repair so that when cells are preinduced PDE might be inhibited prematurely.

DNA Damage↗
PubMed1996

Constitutive increase of RecA protein: its influence on pyrimidine dimer excision and survival of UV-irradiated Escherichia coli.

Transformation of E. coli with the plasmid pRA containing recA gene increased the constitutive level of RecA protein 50-67 fold. This slightly inhibited pyrimidine dimer excision and reduced cell survival in three investigated, UV-irradiated E. coli strains. Our data support the view that RecA protein prematurely present at a high level may mask the dimers. The masking subsequently reduces the dimer excision and switches off the inducing signal.

DNA, Bacterial↗
PubMed1995

Inducible stable DNA replication of Escherichia coli tolerates unexcised pyrimidine dimers in an uvr-dependent manner.

Damage-inducible DNA replication (iSDR) was followed in UV-irradiated E. coli uvr+ and uvr B5 cells. Owing to the inhibition of dimer excision in the former (caused by the metabolic treatment), both contained similar amounts of unexcised dimers. Since the iSDR took place in uvr+ but not in uvr B5 cells, it is concluded that the uvr system can tolerate unexcised dimers through the recombinogenic iSDR.

DNA Damage↗
PubMed1995

DNA repair in Escherichia coli: the dual function of uvr genes.

It has been shown earlier that the starvation of E. coli for both amino-acids and thymine applied prior to UV irradiation inhibits pyrimidine dimer excision without affecting cell survival after UV irradiation. In such cells pyrimidine dimers are tolerated by a rather error-free process that depends on the activity of uvrB, recA and lexA genes. Data presented here show: (a) that the efficient toleration of unexcised dimers requires also the uvrA gene; (b) that the starvation increases the level of RecA protein about 4.7 times; (c) that the effect of starvation on subsequent pyrimidine dimer excision is reversed by a 2 h incubation in complete medium before the cells are UV irradiated. The data suggest that the uvrA, uvrB, recA, lexA dependent nonexcisional repair may be a pathway temporarily functioning in repeatedly damaged cells.

Adenosine Triphosphatases↗
PubMed1993

Enhancement of the uvrA gene dosage reduces pyrimidine dimer excision in UV-irradiated Escherichia coli.

E. coli possesses an efficient repair mechanism able to remove pyrimidine dimers from UV-irradiated DNA, which is catalyzed by UvrABC endonuclease. In E. coli B/r Hcr+ cells transformed with a multicopy plasmid harboring a gene coding for UvrA, the excision capacity was greatly reduced. The course of thymine dimer excision was investigated using the enzymatic as well as the radiochromatographic method and the results are discussed in term of nonspecific interaction between the excess of UvrA protein and undamaged DNA duplex.

DNA Repair↗
PubMed1993

Inhibition of dimer excision in repeatedly UV-irradiated Escherichia coli: its requirement for RecA protein and de novo protein synthesis.

In UV-irradiated Escherichia coli dimer excision was found to be inhibited by predamage (M. Sedliaková, F. Masek and J. Brozmanová, FEBS Lett., 23 (1972) 325-326) or overproduction of RecA protein, which suggests that the coating of the dimers by this protein may make them inaccessible to the excision nuclease (M. Sedliaková, K. Kleibl and F. Masek, Mutat. Res., 191 (1987) 13-16). We measured the levels of RecA protein and dimer excision in cells irradiated with (i) a single dose of 50 J m-2, (ii) two separate doses of 30 and 50 J m-2, post-incubated with chloramphenicol; (iii) two separate doses of 30 and 50 J m-2, post-incubated without chloramphenicol. Dimer excision was complete in the first two cases, but in the latter it was inhibited by 40%. At the time of active dimer excision, there were marked differences in RecA protein content between the cells irradiated with a single dose and cells irradiated with two separate doses (both post-incubated without chloramphenicol), which might account for the differences in dimer excision. However, relatively small differences in RecA protein content were found in cells irradiated with two doses and post-incubated with or without chloramphenicol, which could therefore not account for the differences in dimer excision. The data suggest that the inhibition of dimer excision involves some short-lived component(s) other than RecA protein.

Bacterial Proteins↗
PubMed1993

UmuC product contributes to the inhibition of dimer excision produced by thymine-less-amino acid-less pretreatment in UV-irradiated Escherichia coli.

In UV-irradiated Escherichia coli, predamaged by thymine-amino acid starvation or a UV predose, a large amount of dimers may remain unexcised and may be tolerated by an error-free mechanism, which requires the function of uvr, recA and lexA genes. A possible role of the umuC gene in both the inhibition of dimer excision and the toleration of unexcised dimers is investigated. Data suggest that the UmuC gene product is not absolutely necessary for the inhibition of dimer excision in UV-irradiated thymine-less-amino acid-less pretreated cells, but that it contributes to it. However, the UmuC product does not seem to be involved in the toleration of unexcised dimers which is dependent on uvr, recA and lexA.

Bacterial Proteins↗
PubMed1992

Inducible stable DNA replication in Escherichia coli uvr+ and uvr- cells, treated with genotoxic chemicals.

Inducible stable DNA replication (iSDR) provoked by a damaging treatment with MMS, MNU, MNNG, NFAA, NFN, 4NQO, NAL or MMC, was followed in both repair-competent E. coli PQ35 and its uvrA derivative E. coli PQ37. In contrast to SOS-inducible mutagenesis, which is more pronounced in excision-deficient cells, iSDR was more obvious in repair-competent cells. This may be due to special features of iSDR and need not indicate involvement of the uvrA gene product in it.

4-Nitroquinoline-1-oxide↗
PubMed1992

A recA-ada hybrid gene inducible by DNA damage.

A damage-inducible expression vector was constructed in which the original recA structural gene was replaced by the protein-coding region of the ada gene. The O6-alkylguanine-DNA alkyltransferase encoded by the ada gene can be measured by a rapid and highly sensitive assay. The introduction of this construct into an appropriate host cell provides an effective bacterial assay for genotoxins.

Cloning, Molecular↗
PubMed1989

Repression of damage-inducible (din) genes by the lexA3 mutation or by plasmid carrying the lexA gene; effect on pyrimidine dimer excision in UV-irradiated Escherichia coli.

Dimer excision was followed in Escherichia coli K-12 AB1157 DM49 lexA3 mutant (whose repressor is not cleavable with RecA protease), and in E. coli K-12 AB2497[pGC3] carrying the cloned lexA gene. In either case din genes could not be efficiently derepressed. In such cells ultraviolet (UV) irradiation caused an extensive DNA degradation, which was not observed in cells with derepressed din genes. Even after a high UV dose (70 J/m2) dimers were being excised efficiently. However, progressive DNA degradation interfered with the precise detection of unexcised dimers. We conclude that induction of din genes is required for filling some of the gaps and for prevention of DNA degradation, but not for excision itself.

Bacterial Proteins↗
PubMed1989

In UV-irradiated Escherichia coli PQ35 overproducing the RecA protein, expression of the sfiA gene and dimer excision are alleviated.

Escherichia coli PQ35 cells carrying the sfiA-::lacZ operon fusion were transformed either with a multicopy plasmid containing the recA gene (pHSG262 recA) or with a multicopy plasmid alone (pHSG262). Both transformants were UV irradiated. Then induction of the sfiA gene and dimer excision were followed. Amplification of the recA gene partly inhibited both sfiA gene induction and dimer excision. The following interpretation of this phenomenon is proposed. When the RecA protein is in abundance, pyrimidine dimers are quickly masked by it. The masked dimers are less efficiently distinguished by excision nuclease and do not provide the induction signal. Due to this, induction of the sfiA gene as well as dimer excision are inhibited early.

Bacterial Proteins↗
PubMed1987

Inhibition of pyrimidine dimer excision in ultraviolet-irradiated Escherichia coli overproducing RecA protein.

Escherichia coli Br Hcr+ cells transformed with the recombinant multicopy plasmid pBR322 carrying recA gene contain increased amounts of RecA protein. When these cells were UV-irradiated, excision of pyrimidine dimers was reduced by about 50%. It is suggested that the damaged DNA strands may be coated with RecA protein which makes them insensitive to the action of the uvrABC excision nuclease.

DNA Repair↗
PubMed1984

Error-free uvr+-dependent inducible DNA repair in Escherichia coli B/r Hcr+ cells.

The frequency of suppressor (tryptophan reversions) and of true (streptomycin-resistant and dependent) mutations has been followed in E. coli cells irradiated with a single dose or two separate doses of ultraviolet (U.V.) radiation. Under these conditions dimers were efficiently excised after a single dose, while about 40 per cent of the dimers remained unexcised after two doses. Although the level of unexcised dimers in the latter case increased proportionally with the second U.V. dose, the mutation frequency increased by 1.5-2-fold, but did not continue to increase with the level of unexcised dimers. A comparison of excision-proficient and excision-deficient cells containing similar amounts of persisting dimers has shown that proficient cells can tolerate a high level of dimers without an adequate increase in mutation frequency. Our results suggest the existence of an error-free uvr+-dependent inducible repair in E. coli B/r Hcr+ cells.

Cell Survival↗
PubMed1982

Inducible nature of tolerance to lesions produced by ultraviolet light in DNA of Chinese hamster V79 cells.

Chinese hamster V79 cells irradiated by split doses of ultraviolet light (2.5 + 5.0 J m-2) synthesize higher molecular weight DNA molecules than those irradiated by a single dose (5.0 or 7.5 J m-2). A second dose applied 8 h following the first one results in a higher portion of higher molecular weight molecules both in relative and absolute terms. Molecular weight of DNA pulse-labeled 8 h after a dose of 2.5 J m-2 is moderately higher than that of pulse-labeled DNA in unirradiated cells, even after the DNA synthesis in preirradiated cells has been fully recovered. Since the amount of DNA synthesized during the 8 h time interval between the two doses is not lower than that of DNA synthesized during an equal period in unirradiated cells, the synthesis of higher molecular weight molecules is not likely to represent elongation of part of the replicons, the other part being blocked. It is supposed that the induction produced by the first dose is involved in the replication of the damaged template.

Animals↗
PubMed1981

Evidence that dimers remaining in preinduced Escherichia coli B/r Hcr+ become insensitive after DNA replication to the extract from Micrococcus luteus.

In Escherichia coli B/r Her+ irradiated with two separate fluences, dimer excision is prematurely interrupted. The present study was designed to follow tha fate of dimers remaining unexcised. The results imply that these dimers (or distortions containing dimers) are transformed on replication from the state of sensitivity to the state of insensitivity to endonuclease from Micrococcus luteus. This conclusion is based on the following findings: (a) dimers were radiochromatographically detectable in DNA replicated after UV, which indicated that they were tolerated on replication. (b) Similar amounts of dimers were detected radiochromatographically both in DNA remaining unreplicated and DNA twice replicated after UV, This along with the low transfer of parental label into daughter DNA, indicated that dimers remained in situ in parental chains. (c) Immediately after UV, all parental DNA contained numerous sites sensitive to the extract from M. luteus. 2 h after UV, a portion of parental DNA still contained a number of endonuclease-sensitive (Es) sites, while another portion of parental DNA and all daughter DNA were free of Es sites. (d) The occurrence of parental DNA free of Es sites was not temporally correlated with dimer excision, but with the first round of DNA replication. (e) The amount of DNA free of Es sites corresponded to the amount of replicated DNA. (f) Separation of replicated and unreplicated DNA, and detection of Es sites in both portions separately showed that the replicated DNA was almost free of Es sites, whereas unreplicated DNA contained a number of such sites.

DNA Replication↗