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  • 1
    Digitale Medien
    Digitale Medien
    The link between 20S proteasome activity and post-replication DNA repair in Saccharomyces cerevisiae (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 49 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: We have shown previously that deletion of the Saccharomyces cerevisiae UMP1 gene encoding the 20S proteasome maturase causes sensitivity to UV radiation. In the current report, we have extended this finding to show that mutations specifically compromising chymotrypsin-like or trypsin-like activity of 20S proteasome peptidases also result in increased UV sensitivity. We have also established that mutations affecting proteasome activity, namely ump1Δ, pre2-K108R and pup1-T20A, result in spontaneous and UV-induced mutator phenotypes. To elucidate the origin of these DNA repair phenotypes of the proteasomal mutants, we performed epistasis analysis, with respect to UV sensitivity, using yeast strains with the UMP1 deletion in different DNA repair backgrounds. We show that UMP1 is not epistatic to RAD23 and RAD2, which are involved in the nucleotide excision repair (NER) pathway. Instead, our results indicate that UMP1 as well as PUP1 and PRE2 (encoding catalytic subunits of 20S proteasome) belong to an epistatic group of genes functioning in post-replication DNA repair (PRR) and are hypostatic to RAD18, which, in complex with RAD6, plays a central role in PRR. We also show that UMP1 is epistatic to REV3 and RAD30, although the relationship of UMP1 with these genes is different.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03635.x
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  • 2
    Digitale Medien
    Digitale Medien
    The antimutagenic effect of a truncated ε subunit of DNA polymerase III inEscherichia coli cells irradiated with UV light (1995)
    Springer
    Molecular genetics and genomics 247 (1995), S. 216-221 
    Details
    ISSN: 1617-4623
    Schlagwort(e): UV mutagenesis ; DNA polymerase III ε subunit ; UmuDC ; dnaQ49
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract It has previously been suggested that inhibition of the proofreading 3′-5′ exonuclease activity of DNA polymerase may play an important role in generation of UV-induced mutations inEscherichia coli. Our previous work showing that overproduction of ε, the proofreading subunit of DNA polymerase III, counteracts the SOS mutagenic response ofE. coli seemed to be consistent with this hypothesis. To explore further the nature of the antimutagenic effect of ε we constructed plasmid pMK17, which encodes only two of the three highly conserved segments of ε — Exol and ExoII; the third segment, ExoIII, which is essential for 3′–5′ exonuclease activity, is deleted. We show that at 40°C, over-production of the truncated e subunit significantly delays production of M13 phage, suggesting that the protein retains its capacity to bind to DNA. On the other hand, the presence of pMK17 in atrpE65 strain growing at 40°C causes a 10-fold decrease in the frequency of UV-induced Trp+ mutations. This antimutagenic effect of the truncated s is effectively relieved by excess UmuD,C proteins. We also show that the presence of plasmid pIP21, which contains thednaQ49 allele encoding an ε subunit that is defective in proofreading activity, almost completely prevents generation of UV-induced mutations in thetrpE65 strain. We propose that the DNA binding ability of free ε, rather than its 3′–5′ exonuclease activity, affects processing of premutagenic UV-induced lesions, possibly by interfering with the interaction between the UmuC-UmuD′-RecA complex and Pol III holoenzyme. This interaction is probably a necessary condition for translesion synthesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00705652
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  • 3
    Digitale Medien
    Digitale Medien
    Effect of proofreading anddam-instructed mismatch repair systems on N4-hydroxycytidine-induced mutagenesis (1982)
    Springer
    Molecular genetics and genomics 186 (1982), S. 411-418 
    Details
    ISSN: 1617-4623
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The role of the proofreading (3′→5′ exonuclease) function of T4 DNA polymerase and the mismatch repair system ofE. coli on N4-hydroxycytidine (oh4Cyd)1 induced mutagenesis was investigated. oh4Cyd-induced mutation is strongly suppressed when the proofreading activity increases as a result of the presence oftsCB87-antimutator polymerase or elevated temperature (43° C vs 30° C). Mutagenic activity of oh4Cyd, however, is little, if at all, affected by the presence of thetsLB56 mutator allele of T4 DNA polymerase with suppressed proofreading activity. This leads to the conclusion that oh4C nucleotides are not frequently removed by proofreading activity of wild-type T4 DNA polymerase. The number of mutations induced by oh4Cyd increases 3- to 5-fold due to damage of the genesmutS,mutL,uvrE, but notmutR.Dam - cells are more sensitive to, and hypermutable by, oh4Cyd in comparison withdam + cells. This is compatible with the notion that oh4C residues are recognised and excised by mismatch repair enzymes. The results indicate thath neither the proofreading function of T4 DNA polymerase, nor the mismatch repair enzymes, are responsible for the high specificity of oh4Cyd which causes AT→GC transition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00729462
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  • 4
    Digitale Medien
    Digitale Medien
    In vivo effect of DNA repair on the transition frequency produced from a single O6-methyl-or O6-n-butyl-guanine in a T:G base pair (1988)
    Springer
    Molecular genetics and genomics 213 (1988), S. 325-331 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Site-specific mutagenesis ; O6-alkyl-guanine ; Transitions from T:MeG and T:BuG ; DNA repair ; Bacteriophage ΦX174
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary We have previously reported some effects of DNA repair on the transition frequencies produced by an O6-methyl-guanine (MeG) or an O6-n-butyl-guanine (BuG) paired with C at the first position of the third codon in gene G of bacteriophage ΦX174 form I'DNA (Chambers et al. 1985). We now report experiments in which the transition is produced from T:MeG or T:BuG, instead of C:MeG or C:BuG, located at this site. The site-modified DNAs were transfected into cells with normal DNA repair as well as into cells with repair defects (uvrA, uvrB, uvrC, recA, uvrArecA). The lysates were screened for phage carrying the expected transition using a characteristic change in phenotype. The data demonstrate that the transition frequency from T:BuG is low (0.3% of total phage progeny) in cells with normal repair (Escherichia coli AB1157) and increases 7-fold in uvrA cells (E. coli AB1886). A similar increase is seen in uvrB and uvrC cells (AB1885, AB1884). These data, like our previous data, indicate BuG is repaired primarily by excision. In contranst to this, the transition frequency from T:MeG is high (5±2%) in cells with normal repair. After induction of alkyl transfer repair in E. coli AB1157, the transition frequency goes up 5-fold. Compared with cells with normal repair, the transition frequency goes up 2-fold in uvrA, uvrB and uvrC cells; it goes up 1.5-fold in recA cells (E. coli AB2463). The data reinforce our earlier conclusion that MeG is repaired primarily by alkyl transfer, but the ABC excinuclease as well as RecA protein inhibit this repair process. Using the BuG data reported here and in our previous paper, we calculate that BuG pairs with a thymine residue 0.5%–0.62% of the time during replication in vivo, and that BuG markedly inhibits replication of the strand that contains it. Because of the complication introduced by alkyl transfer repair, similar calculations for MeG cannot be made from the current data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00339598
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  • 5
    Digitale Medien
    Digitale Medien
    Alternative pathways of methyl methanesulfonate-induced mutagenesis in Escherichia coli (1989)
    Springer
    Molecular genetics and genomics 216 (1989), S. 126-131 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Methyl methanesulfonate mismatch repair ; Mutagenesis ; Suppressive mutations ; Escherichia coli
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Methyl methanesulfonate (MMS) induced mutagenesis is known to be largely dependent on functional umuCD and recA genes. By phenotypic analysis of Arg+ (argE3, ochre) revertants according to their reversion of the mutations his-4 (ochre) and thr-1 (amber), we attempted to deduce the specificity and/or sites of MMS-induced mutations. It is shown that: (1) MMS-induced, umuC-dependent Arg+ revertants (which prevail in bacteria proficient in mismatch repair) result from a different mutational pathway from umuC-independent ones. UmuC-dependent Arg+ revertants belong to class 2 (Arg+His+Thr−), and umuC-independent ones to class 1 (Arg+His−Thr−). (2) The mismatch repair system very efficiently prevents mutations induced by MMS. We found that in the mutS strain, deficient in mismatch repair, class 1 Arg+ revertants are the most numerous, whereas class 2 Arg+ revertants occur at similar levels in MMS-treated mutS and mutS + strains. Therefore the mismatch repair system very efficiently prevents formation of umuC-independent Arg+ revertants, but exerts negligible or no effect on umuC-dependent Arg+ revertants. (iii) Both mutS umuC and mutS recA strains, are highly mutable by MMS.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00332240
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  • 6
    Digitale Medien
    Digitale Medien
    Different UmuC requirements for generation of different kinds of UV-induced mutations in Escherichia coli (1994)
    Springer
    Molecular genetics and genomics 243 (1994), S. 584-592 
    Details
    ISSN: 1617-4623
    Schlagwort(e): dnaQ49 ; UmuDC proteins ; Mutant umuC plasmids ; Specificity of UV mutagenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract An Escherichia coli strain bearing the dnaQ49 mutation, which results in a defective s subunit of DNA polymerase III, and carrying the lexA71 mutation, which causes derepression of the SOS regulon, is totally unable to maintain high-copy-number plasmids containing the umuDC operon. The strain is also unable to maintain the pAN4 plasmid containing a partial deletion of the umuD gene but retaining the wild-type umuC gene. These results suggest that a high cellular level of UmuC is exceptionally harmful to the defective DNA polymerase III of the dnaQ49 mutant. We have used this finding as a basis for selection of new plasmid umuC mutants. The properties of two such mutants, bearing the umuC61 or umuC95 mutation, are described in detail. In the umuC122:: Tn 5 strain harbouring the mutant plasmids, UV-induced mutagenesis is severely decreased compared to that observed with the parental umuDC + plasmid. Interestingly, while the frequency of UV-induced GC → AT transitions is greatly reduced, the frequency of AT → TA transversions is not affected. Both mutant plasmids bear frameshift mutations within the same run of seven A residues present in umuC +; in umuC61 the run is shortened to six A whereas in umuC95 is lengthened to eight A. We have found in both umuC61 and umuC95 that translation is partially restored to the proper reading frame. We propose that under conditions of limiting amounts of UmuC, the protein preferentially facilitates processing of only some kinds of UV-induced lesions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00284207
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