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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Retrons are genetic elements that encode multicopy single-stranded DNAs called msONAs. They are clonally distributed in Escherichia coli and retrons in different clones produce DNAs with different nucleotide sequences. msDNAs consist of an RNA molecule covalently linked to a single-stranded DNA molecule. The latter contains an inverted repeat, resulting in a stem-loop structure. In two retrons, Ec83 and Ec78, the DNA is cleaved off from the RNA. All known retrons except Ec78, have one or more mismatched base pairs in the stem-loop structure. We found that two retrons, Ec86 and Ec83, when present in high copy numbers are mutagenic. The ratios of mutation frequencies observed in Lac indicator strains were similar to the ratios observed for a mutant defective in mismatch repair. It is known that some proteins required for mismatch repair bind to mismatched base pairs prior to carrying out repair. The similarity in the mutation frequency ratios suggested that the mutagenesis caused by msDNAs of retrons Ec86 and Ec83 might be due to seqestration of a mismatch repair protein by msDNA. Strong support for this interpretation was obtained from the finding that the msDNA produced by retron Ec78 is not mutagenic.
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  • 2
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The growth of E. coli K12 strains derepressed for N-α-acetyl-L-ornithinase (the argE gene product) is inhibited by 25 mg/ml N-α-acetyl-DL-norvaline. This is due to deacetylation of acetylnorvaline by acetylornithinase yielding norvaline which inhibits growth. A genetically repressible (argR +) strain (514) in which acetylornithinase is repressed is resistant. Thus, acetylnorvaline resistance can be used to select argR + recombinants and transductants from a genetically derepressed (argR -) strain (514-1). ArgR - strains lacking acetylornithinase activity are resistant to acetylnorvaline. Strain 514-1-34 (argR -) which is completely deleted for argE is resistant. Also, of 52 spontaneous acetylnorvaline-resistant mutants derived from strain 514-1, 45 were argE -.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Transducing λ bacteriophages have been isolated which carry the divergently transcribed argECBH operon of E. coli K12 and various portions of the adjacent ppc and bfe chromosomal regions. They were recovered from lysates prepared by the procedure of Schrenk and Weisberg using a Ppc+ Arg+ Bfe+ strain carrying a deletion of the usual attachment site of λ. Heteroduplex DNA mapping of these λdarg and of the ϕ80 darg isolated by B. Konrad indicates that the two kinds of phages carry the arg cluster in opposite orientations, a situation favorable for the isolation of argECBH DNA. A physical map of the ppc argECBH bfe region including 2 unusual attachment sites of λ has been constructed. The localization of the end points of certain arg deletions provides a useful reference framework for the currently pursued mapping of mutations affecting the control of divergent transcription and for the location of restriction enzyme cleavage sites in the arg region.
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  • 4
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A fused F prime factor was obtained from a mating of arecA donor carrying an F' factor containing the genesmetBJF, ppc andargECBH (KLF5) with arecA recipient carrying an F' factor containingatt80, trp andlac (F155). Lysogenization of this fused F-prime factor with λcI857 hϕ80 phage followed by thermoinduction produced the transducing phages ϕ80dmetBJF and ϕ80dppcargECBH. This kind of fusion provides a general procedure for the construction of transducing phages carrying genes from different regions of theE. coli genome. To understand the mechanism of this fusion, the parental F prime factors (F155 and KLF5) were analyzed by the electron microscope heteroduplex technique. F155 has a length of 176±3 kilobases including two substitutions. The F sequence 0 F-2.8 F has been substituted by 53 kb of chromosomal DNA including thelac operon and the F sequences 8.5 F-16.3 F has been substituted by 27 kb of a chromosomal sequence includingatt80 and thetrp operon. KLF5 contains 221±4 kilobases of DNA (molecular weight, 148 megadaltons). It contains complete F and the segment of theE. coli chromosome frompolA torif. The F sequence 2.8 F-8.5 F known to be involved in F specific recombination inrecA + andRecA backgrounds occurs twice on KLF5, once at each of the junctions of F DNA with chromosomal DNA. The population of closed circular plasmid molecules extracted from KLF5-containing strains is heterogeneous. It is proposed that this heterogeneity is due to intramolecular recombination events occurring in KLF5 between the duplicated 2.8 F-8.5 F sequences. Such recombination can account for the genetic instability of KLF5 observed in bothrecA + andrecA hosts. The F sequence 2.8 F-8.5 F (also called γδ) is one of the characterized integration sequences on F. A model for the fusion of the parental F prime factors is proposed in which recombination between γδ sequences bringsatt80 close to themetBJF genes. This is followed by a deletion of an F'lac factor. The resulting fused F' factor still carries two γδ sequences and is therefore expected to be unstable. The closed circular molecules isolated from the fused F' containing strains show two different sizes of molecules. Genetic and physical analyses of these molecules are in agreement with the predicted instability of the fused F' factor and the existance of the γδ sequence in the ϕ80dmet phages isolated from fused F' and previously analyzed by the electron microscope heteroduplex technique.
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  • 5
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants of Escherichia coli K-12 previously isolated in the authors' laboratory have reduced arginyl-tRNA synthetase activity. The mutants fall into two classes. All mutants grow slowly on arginine-free medium. On arginine-supplemented medium some mutants grow at a normal rate (Class I) while others still grow slowly (Class II). Matings were performed to located a Class I and a Class II mutation on the E. coli chromosome map, and on the basis of our results we have assigned both to one locus, argS.
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  • 6
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The expression of a newly transferred lacZ + gene in lacZ recipients carrying various mutations in the recA and recB genes was studied by measuring the rates of induced synthesis of β-galactosidase in zygotes formed after mating with either F′ or Hfr donors. The ability to synthesize β-galactosidase decreases with time in both recA and recB zygotes when the lacZ + gene is transferred from an Hfr donor, but not when the lacZ gene is transferred from an F′ donor. There is no such inactivation of the newly transferred lacZ + gene in Rec+ zygotes. We conclude that the functioning of the transferred DNA is progressively inactivated in rec recipients unless the DNA is contained in an episome such as F′.
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  • 7
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Φ80dargECBH DNA has been used to direct cell-free synthesis of argininosuccinase, the argH gene product in Escherichia coli K12. In vitro enzyme synthesis is sensitive to repression by partially purified preparations from an argR + strain but not by corresponding preparations from an argR - strain. Using DNA-cellulose chromatography, approximately seventyfold purification of repressor has been obtained. The partially purified preparation represses argininosuccinase synthesis but has no effect on β-galactosidase synthesis.
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  • 8
    ISSN: 1617-4623
    Keywords: Replicon interactions ; Bireplicon plasmids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Many plasmids belonging to the F incompatibility groups contain more than one basic replicon. The chimeric plasmid pCG86 is an example of such a multireplicon plasmid. The two basic replicons of pCG86, RepFIIA/FIC and RepFIB have been cloned and re-ligated, the copy numbers of the clones have been determined, and the incompatibility behavior of plasmids containing the ligated replicons and the individual replicons has been studied. The bireplicon plasmids are not expected to be incompatible as recipients with monoreplicon RepFIB or RepFIIA/RepFIC plasmids, since when one replicon is challenged by an incoming replicon, the other should be able to handle the plasmid's replication. In our studies, we found that challenge with either monoreplicon plasmid resulted in incompatibility. This incompatibility was increased in bireplicon plasmids in which RepFIB was duplicated. We conclude that in the bireplicon plasmids, challenging the replication control of one replicon by an incompatible plasmid can interfere with the replication originating from the second replicon.
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Multicopy single-stranded DNA (msDNA) molecules consist of single-stranded DNA covalently linked to RNA. In Escherichia coli, such molecules are encoded by genetic elements called retrons. The DNA moieties of msDNAs have characteristic stem-loop structures, and most of these structures contain mismatched base pairs. Previously, we showed that retrons encoding msDNAs with mismatched base pairs are mutagenic when present in multicopy plasmids. In this study we show that such msDNAs, in a similar manner to genetic defects in mismatch repair, increase the frequency of interspecies recombination in matings between Salmonella typhimurium and E. coli. To demonstrate interference with mismatch repair by msDNA, we show that the addition of a plasmid containing the gene for MutS protein suppresses the mutagenic and recombinogenic effects of msDNAs. We also show that in mutS mutants, msDNA does not increase the frequency of either mutations or interspecies recombination. We conclude from these findings that the mutagenic and recombinogenic effects of msDNAs are due to titrating out MutS protein.
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 71 (1949), S. 1865-1865 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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