Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A new type of Escherichia coli mutant which shows increased sensitivity to methyl methane sulfonate but not to UV light or to gamma rays was isolated after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. The mutant is unable to reactivate phage lambdavir or double-stranded phiX174 DNA (replicative form) that had been treated with methyl methane sulfonate. The mutant is sensitive to other alkylating agents, such as ethyl methane sulfonate, mitomycin C, and N-methyl-N'-nitro-N-nitrosoguanidine, as well. It grows normally and exhibits almost normal recombination proficiency. The mutant possesses normal levels of DNA polymerase I, exonuclease I, exonuclease V, endonuclease specific for methyl methane sulfonate-treated DNA, and 3-methyladenine-DNA glycosidase activities. The genetic locus responsible has been named alk and is located near his on the chromosome.
 ...
PMID:Escherichia coli gene that controls sensitivity to alkylating agents. 35 28

Using the single-stranded circular DNA of bacteriophage fd as template, double-stranded circular DNA has been prepared in vitro with either 5-hydroxymethylcytosine ([hmdC]DNA) or cytosine ([dC]DNA) in the product strand. Extracts prepared from Escherichia coli cells restrictive to T-even phage containing nonglucosylated DNA degrade [hmdC]DNA to acid-soluble material in vitro, but do not degrade [dC]dna. In contrast, extracts prepared from E. coli K12 rglA- rglB-, a strain permissive to T-even phage containing nonglucosylated DNA, do not degrade [hmdC]DNA or [dC]DNA. In addition, glucosylation of the [hmdC]DNA renders it resistant to degradation by extracts from restrictive strains. The conversion of [hmdC]DNA to acid-soluble material in vitro consists of an HmCyt-specific endonucleolytic cleavage requiring the presence of the RglB gene product to form a linear molecule, followed by a non-HmCyt-specific hydrolysis of the linear DNA to acid-soluble fragments, catalyzed in part by exonuclease V. The RglB protein present in extracts of E. coli K12 rglA- rglB+ has been purified 200-fold by complementation with extracts from E. coli K12 rglA- rglB-. The purified RglB protein does not contain detectable HmCyt-specific endonuclease or exonuclease activity. In vitro endonucleolytic cleavage of [hmdC]DNA thus requires additional factors present in cell extracts.
 ...
PMID:Modification and restriction of T-even bacteriophages. In vitro degradation of deoxyribonucleic acid containing 5-hydroxymethylctosine. 76 37

DNA molecules that have been damaged in both strands at the same level are not subject to repair by excision but instead can be repaired through recombination with homologous molecules. Examples of two-strand damage include postreplication gaps opposite pyrimidine dimers, two-strand breaks produced by X-rays, and chemically induced interstrand cross-links. In ultraviolet-irradiated bacteria, the newly synthesized DNA is of length equal to the interdimer spacing. With continued incubation, this low-molecular-weight DNA is joined into high-molecular-weight chains (postreplication repair), a process associated with sister exchanges in bacteria. Recombination is initiated by pyrimidine dimers opposite postreplication gaps and by interstrand cross-links that have been cut by excision enzymes. The free ends at the resulting gaps presumably initiate the exchanges. Postreplication repair in Escherichia coli occurs in recB- AND RECC but is greatly slowed in recF- mutants. RecB and recC are the structural genes for exonuclease V, which digests two-stranded DNA by releasing oligonucleotides first from one strand and then from the other. The postreplication sister exchanges in ultra-violet-irradiated bacteria result in the distribution of pyrimidine dimers between parental and daughter strands, indicating that long exchanges involving both strands of each duplex occur. The R1 restriction endonuclease from E. COli has been used to cut the DNA of a bacterial drug-resistance transfer factor with one nuclease-sensitive site, and also DNA from the frog Xenopus enriched for ribosomal 18S and 28S genes. The fragments were annealed with the cut plasmid DNA and ligated, producing a new larger plasmid carrying the eukaryotic rDNA and able to infect and replicate in E. coli.
 ...
PMID:Repair by genetic recombination in bacteria: overview. 110 33

In UV-irradiated cells of Escherichia coli K-12 a partial release of the restriction of non-modified phage lambda is observed when the cells are recA+ lexA+. We show here that the induction of this restriction allevation (RA) also depends on the recBC enzyme and that the expression of RA requires protein synthesis. Maximum expression was reached within 60 to 90 min after irradiation. Experiments are presented which show that upon UV-irradiation a signal is created which triggers the development of RA when protein synthesis is allowed. This signal decayed with a half-life of only a few minutes in cells treated with chloramphenicol. The decay kinetics were similar in uvr+ and uvrA mutants. RA appeared to be specific for EcoK insofar as no allevation of lambda restriction by EcoRI, EcoRII and EcoP1 occurred. During maximum expression of RA no gross reduction of the activities of the recBC enzyme (exonuclease V) and the restriction endonuclease EcoK was observed and no new DNA modifying activity appeared in the cells. Since, in fully expressed cells, up to 75% of the infecting lambda DNA was converted to acid-soluble material within 20 min after infection we suggest that only a small specific fraction of lambda infections may undergo RA.
 ...
PMID:UV-induced allevation of lambda restriction in Escherichia coli K-12: kinetics of induction and specificity of this SOS function. 621 35

Exonuclease VIII is an enzyme whose synthesis is induced as a result of sbcA mutations. The enzyme has been purified to near homogeneity from an Escherichia coli strain containing an sbcA mutation and mutations in the structural genes for exonuclease III, exonuclease V, and endonuclease I. The enzyme specifically degrades linear duplex DNA in a reaction which requires magnesium ions and is susceptible to inhibition by other divalent cations and by sulfhydryl-blocking reagents. Enzyme activity occurs over a broad pH range with peak activity at pH 8.5 in Tris buffer. The protein has a subunit Mr = 140,000, a sedimentation coefficient of 8.4 +/- 0.6, and a Stokes radius of 142 +/- 6 A, which is consistent with its active form being a multimer. Exonuclease VIII has a frictional coefficient of 2.6 which indicates that it has an asymmetric structure.
 ...
PMID:Exonuclease VIII of Escherichia coli. I. Purification and physical properties. 635 Feb 89

Preparation of an in vitro coupled transcription-translation system from E. coli strains lacking exonuclease V has greatly improved the system for use with added linear DNA fragments. In fact, in extracts of these mutants linear fragments are stable for several hours. However the cell extracts show a high level of endogenous background. To avoid this complication extracts were prepared at 30 degrees C from a mutant carrying a temperature-sensitive exonuclease V. Polypeptides coded by a specific DNA region, e.g., delineated by restriction endonuclease sites, can now be easily identified.
 ...
PMID:Enhanced polypeptide synthesis programmed by linear DNA fragments in cell-free extracts lacking exonuclease V. 635 55

A review of the data on the genetic determination of general recombination in Escherichia coli introduces three alternative pathways of recombination, RecBC, RecF, and RecBCF. One recBC-dependent pathway is functional in recF- cells. An initiating endonuclease is involved, acting on the chi-sites of DNA. The second is recF-dependent, acting in the double mutant recBC sbcB. The corresponding endonuclease uses the fre-sites as a substrate. A third pathway acting in wild-type cells is mixed. Both enzymatic systems participate in the overall process. We shall call it RecBCF. Using the thermosensitive recA44 mutant it became possible to study the kinetics of integration of donor DNA into the recipient chromosome via the RecF and RecBCF pathways of recombination. The RecF pathway is characterized by delayed recombination; not less than 14 h being needed to complete the process at 35 degrees C. By the RecBCF pathway (wild-type recipient) the reaction is fast, as described by Lloyd and Johnson (1979). The two stage nature of the RecF pathway is important. First an intermediate product is formed during a short time interval. This product is resistant to the degrading exonuclease V. Afterward the intermediate product is slowly integrated into the recipient chromosome. Autoradiography of this intermediate product, extracted from exconjugants, shows that it consists of closed DNA circles. Their length is within the limits 2--15 min on the E. coli map. Their average value is in fair agreement with genetic estimations of the integrated DNA fragments. Taking into consideration the similarity between genetic determinations of the fre-effects and the heterogeneity of the progeny, we conclude that the intermediate structures formed contribute to this heterogeneity.
 ...
PMID:The process of general recombination in Escherichia coli K-12: structure of intermediate products. 703 14

Escherichia coli cell-free protein synthesis is a highly productive system that can be applied to high throughput expression from polymerase chain reaction (PCR) products in 96-well plates for proteomic studies as well as protein evolution. However, linear DNA instability appears to be a major limitation of the system. We modified the genome of the E. coli strain A19 by removing the endA gene encoding the endonuclease I and replacing the recCBD operon (in which recD encodes the exonuclease V) by the lambda phage recombination system. Using the cell extract from this new strain increased the stability of PCR products amplified from a plasmid containing the cat gene. This resulted in CAT (chloramphenicol acetyltransferase) production from PCR products comparable to that from plasmids (500-600 microg/ml) in a batch reaction. We show that cell-free protein synthesis reactions using PCR products amplified from genomic DNA and extended with the T7 promoter and the T7 terminator give the same high yields of proteins (550 microg/ml) in 96-well plates. With this system, it was possible to rapidly express a range of cytoplasmic and periplasmic proteins.
 ...
PMID:Increasing PCR fragment stability and protein yields in a cell-free system with genetically modified Escherichia coli extracts. 1625 43