Hyper-recombination in dam mutants of Escherichia coli K-12

Marinus, Martin; Konrad, E. Bruce

doi:10.1007/bf00268528

Cited by 88 publications

(28 citation statements)

References 10 publications

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“…Nevertheless, these restriction endonucleases have limited applicability for the elucidation of restriction endonuclease patterns. When molecular cloned genes of eukaryotes are propagated on methylation deficient hosts (Marinus & Morris, 1973;Hattman et al, 1973) these DNA sequences can be obtained in the unmethylated form. Thus, the natural state of methylation of these sequences can be determined by cleaving the cellular …”

Section: W Doerflermentioning

confidence: 99%

DNA Methylation--A Regulatory Signal in Eukaryotic Gene Expression

Doerfler

1981

Journal of General Virology

184

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Section: W Doerflermentioning

confidence: 99%

DNA Methylation--A Regulatory Signal in Eukaryotic Gene Expression

Doerfler

1981

Journal of General Virology

184

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“…The frequency of correction in vivo is reduced in mutH, mutL, and mutS bacteria, and the direction of repair is dependent on strand methylation (35). Heteroduplex molecules with 4 unpaired bases are marginally repaired, and those with five unpaired bases are resistant to repair (35).dam-directed mismatch repair is also active in correction of heteroduplex regions formed during recombination, since dam, mutH, mutL, and mutS strains show a hyper-recombination phenotype (12,30). Interspecies crosses between E. coli and Salmonella typhimurium indicate that the damdirected system suppresses formation of heterospecific recombinants (39).…”

mentioning

confidence: 99%

“…dam-directed mismatch repair is also active in correction of heteroduplex regions formed during recombination, since dam, mutH, mutL, and mutS strains show a hyper-recombination phenotype (12,30). Interspecies crosses between E. coli and Salmonella typhimurium indicate that the damdirected system suppresses formation of heterospecific recombinants (39).…”

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confidence: 99%

Repair of heteroduplex DNA molecules with multibase loops in Escherichia coli

Carraway

Marinus

1993

J Bacteriol

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The fate of heteroduplex molecules containing 5-, 7-, 9-, 192-, 410-, and 514-base loops after transformation of wild-type and various mutant strains of Escherichia coli has been examined. No evidence for repair was obtained for the wild type or for strains with mutations in the following genes: mutS, recA, recBC sbcBC, recD, recF, recJ, recN, recO, recR, recBC sbcBC recF uvrA, recG ruvC, ruvB, lexA3, lexASI, uvrA, nfo xth nth, poL4(Ts), or pcnB. These results rule out the involvement of the SOS system and most known recombination and repair pathways. Repair of heteroduplex molecules containing 410-and 514-base loops was observed when a 1-base deletion-insertion mismatch was present nearby. The repair of both the mismatch and the loops was directed by the state ofdam methylation of the DNA chains and was dependent on the product of the mutS gene. A high efficiency of repair (95%) An additional possible fate of a heteroduplex molecule was described by Meselson and coworkers (46,47). When lambda phage heteroduplexes with a base mismatch were transfected into bacterial cells, mixed plaques with both parental genotypes were recovered at a frequency much lower (about 30%) than that expected (i.e., 100%). There was a corresponding increase in plaques with either of the pure parental genotypes. This result can be explained if only one of the two strands of the heteroduplex had been replicated preferentially in the infected cell and if the strand was selected at random. This phenomenon was termed strand loss. The molecular basis for strand loss is unknown.One of the systems that acts on base mismatches in heteroduplex DNA is dam-directed mismatch repair in which the direction of strand correction is determined by the degree of N6-adenine methylation at GATC sequences of the DNA chains (37). In contrast to strand loss, experiments with phage lambda base-mismatch heteroduplexes indicated that correction not only was dependent on strand methylation but also varied widely depending on the mismatch used (31). In addition, repair was confined to a small region of the chromosome not more than a few kilobases in length (47) and was absent in fully methylated heteroduplexes and uvrD and mutL strains of Escherichia coli. Similar results were obtained with phage M13 heteroduplexes which also showed a * Corresponding author. Electronic mail address: dam@ummed. edu.hierarchy of correction efficiency depending on the mismatch (21).The dam-directed repair system of E. coli also corrects with high efficiency heteroduplex molecules with 1, 2, or 3 unpaired bases both in vitro (22) and in vivo (35). The frequency of correction in vivo is reduced in mutH, mutL, and mutS bacteria, and the direction of repair is dependent on strand methylation (35). Heteroduplex molecules with 4 unpaired bases are marginally repaired, and those with five unpaired bases are resistant to repair (35).dam-directed mismatch repair is also active in correction of heteroduplex regions formed during recombination, since dam, mutH, mutL, and mutS strains show a hyp...

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“…The lack of methylation in dam-strains leads to increased frequencies of recombination and spontaneous mutation (2,27,29) and increased sensitivity to methyl methanesulfonate (29) and UV (27). Furthermore, the dam mutation is lethal in combination with recBIC or lexA mutations (2,29).…”

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Expression of the Escherichia coli dam methylase in Saccharomyces cerevisiae: effect of in vivo adenine methylation on genetic recombination and mutation.

Hoekstra¹,

Malone²

1985

Mol. Cell. Biol.

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The Escherichia coli DNA adenine methylase (dam) gene has been introduced into Saccharomyces cerevisiae on a yeast-E. coli shuttle vector. Sau3AI, MboI, and DpnI restriction enzyme digests and Southern hybridization analysis indicated that the dam gene is expressed in yeast cells and methylates GATC sequences. Analysis of digests of total genomic DNA indicated that some GATC sites are not sensitive to methylation. The failure to methylate may reflect an inaccessibility to the methylase due to chromosome structure. The effects of this in vivo methylation on the processes of recombination and mutation in mitotic cells were determined. A small but definite general increase was found in the frequency of mitotic recombination. A similar increase was observed for reversion of some auxotrophic markers; other markers demonstrated a small decrease in mutation frequency. The effects on mutation appear to be locus (or allele) specific. Recombination in meiotic cells was measured and was not detectibly altered by the presence of 6-methyladenine in GATC sequences.Methylation of DNA bases has been demonstrated to play an important role in the processes of DNA replication, repair, and recombination in procaryotes and gene expression in eucaryotes (1, 4). In Escherichia coli a methyl group is added, after replication, to the N6 position of adenine in 5'-GATC-3' sequences by DNA adenine methylase produced by the dam gene (15,28). It has been proposed that the transient undermethylation of newly replicated strands allows a mismatch repair system to preferentially remove the new (incorrect) information when replication errors occur (13,37,42). Recent experiments using heteroduplexes of phage X DNA, methylated in vitro and transformed into E. coli, have confirmed that the mismatched base on the undermethylated strand is preferentially repaired (36).In E. coli, the consequences of losing the ability to methylate adenine are profound. The lack of methylation in dam-strains leads to increased frequencies of recombination and spontaneous mutation (2, 27, 29) and increased sensitivity to methyl methanesulfonate (29) and UV (27). Furthermore, the dam mutation is lethal in combination with recBIC or lexA mutations (2, 29). All of these phenotypes can be understood in terms of the mismatch correction system being unable to distinguish which strand to attack when a mismatch is created during replication. Specifically, increased mutation could occur when the correct base was removed, and increased recombination could result from single-strand gaps and breaks or from double-strand breaks generated when excision tracks on both DNA strands overlap (37). Overproduction of the dam enzyme also leads to increased mutation frequencies (19). Herman and Modrich argued that increased levels of the dam methylase would result in a DNA molecule (19) Table 1. To monitor the effect of dam on recombination, the yeast diploid strain MH16 was constructed containing six heteroallelic loci and two recessive drug resistance loci. The former allow us to examine mi...

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Hyper-recombination in dam mutants of Escherichia coli K-12

Cited by 88 publications

References 10 publications

DNA Methylation--A Regulatory Signal in Eukaryotic Gene Expression

DNA Methylation--A Regulatory Signal in Eukaryotic Gene Expression

Repair of heteroduplex DNA molecules with multibase loops in Escherichia coli

Expression of the Escherichia coli dam methylase in Saccharomyces cerevisiae: effect of in vivo adenine methylation on genetic recombination and mutation.

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