Localization of the gam gene of bacteriophage Mu and characterisation of the gene product

Akroyd, J.; Symonds, N.

doi:10.1016/0378-1119(86)90288-x

Cited by 26 publications

(31 citation statements)

References 18 publications

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“…Each of the three insertion mutants could therefore presumably activate expression of Mu gene gam , which is only 42 bp downstream of the most distal transposon (the one in gene 9 ), by read-through transcription. Gam is normally transcribed as part of an early operon during Mu infection, starting at the P e promoter (42,43), but would not normally be expressed in lysogens (or presumably from the dinD::lacZ construct) (44). The Mu Gam protein inhibits nucleases, including RecBC, by binding to DNA ends (45).…”

Section: Resultsmentioning

confidence: 99%

Functions that protect Escherichia coli from DNA–protein crosslinks

Krasich

Kuo

2015

DNA Repair

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Pathways for tolerating and repairing DNA-protein crosslinks (DPCs) are poorly defined. We used transposon mutagenesis and candidate gene approaches to identify DPC-hypersensitive Escherichia coli mutants. DPCs were induced by azacytidine (aza-C) treatment in cells overexpressing cytosine methyltransferase; hypersensitivity was verified to depend on methyltransferase expression. We isolated hypersensitive mutants that were uncovered in previous studies (recA, recBC, recG, and uvrD), hypersensitive mutants that apparently activate phage Mu Gam expression, and novel hypersensitive mutants in genes involved in DNA metabolism, cell division, and tRNA modification (dinG, ftsK, xerD, dnaJ, hflC, miaA, mnmE, mnmG, and ssrA). Inactivation of SbcCD, which can cleave DNA at protein-DNA complexes, did not cause hypersensitivity. We previously showed that tmRNA pathway defects cause aza-C hypersensitivity, implying that DPCs block coupled transcription/translation complexes. Here, we show that mutants in tRNA modification functions miaA, mnmE and mnmG cause defects in aza-C-induced tmRNA tagging, explaining their hypersensitivity. In order for tmRNA to access a stalled ribosome, the mRNA must be cleaved or released from RNA polymerase. Mutational inactivation of functions involved in mRNA processing and RNA polymerase elongation/release (RNase II, RNaseD, RNase PH, RNase LS, Rep, HepA, GreA, GreB) did not cause aza-C hypersensitivity; the mechanism of tmRNA access remains unclear.

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Section: Resultsmentioning

confidence: 99%

Functions that protect Escherichia coli from DNA–protein crosslinks

Krasich

Kuo

2015

DNA Repair

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“…It has been proposed that Gam's role, following viral infection, is to bind to the ends of linear-phage DNA, preventing degradation by host exonucleases, and thus enhancing integration of the phage genome into the host's chromosome [31]. Interestingly, E. coli (strains expressing Gam, such as O157:H7) takes up linearized plasmid DNA much more efficiently than strains lacking this gene [32]. This strain, as well as other bacteria (e.g., Neisseria meningitidis, Haemophilus influenzae ) possessing a phage-derived Gam, are naturally competent for DNA transformation.…”

Section: Nhej In Prokaryotesmentioning

confidence: 99%

Making Ends Meet: Repairing Breaks in Bacterial DNA by Non-Homologous End-Joining

Bowater¹,

Doherty²

2006

PLoS Genet

182

149

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DNA double-strand breaks (DSBs) are one of the most dangerous forms of DNA lesion that can result in genomic instability and cell death. Therefore cells have developed elaborate DSB-repair pathways to maintain the integrity of genomic DNA. There are two major pathways for the repair of DSBs in eukaryotes: homologous recombination and non-homologous end-joining (NHEJ). Until very recently, the NHEJ pathway had been thought to be restricted to the eukarya. However, an evolutionarily related NHEJ apparatus has now been identified and characterized in the prokarya. Here we review the recent discoveries concerning bacterial NHEJ and discuss the possible origins of this repair system. We also examine the insights gained from the recent cellular and biochemical studies of this DSB-repair process and discuss the possible cellular roles of an NHEJ pathway in the life-cycle of prokaryotes and phages.

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“…Alternatively, the cell may simply heal each break as fast as it is formed, thus solving the problem of which ends to ligate together. In addition, some proteins (Mu Gam, RecA) are known to bind DNA ends and could assist DNA ligase (26,33).…”

Section: Methodsmentioning

confidence: 99%

Repair of the Escherichia coli chromosome after in vivo scission by the EcoRI endonuclease.

Heitman

Zinder

Model

1989

Proc. Natl. Acad. Sci. U.S.A.

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We prepared a set of temperature-sensitive mutants of the EcoRI endonuclease. Under semipermissive conditions, Escherichia coli strains bearing these alleles form poorly growing colonies in which intracellular substrates are cleaved at EcoRI sites and the SOS DNA repair response is induced. Strains defective in SOS induction (lexA3 mutant) or SOS induction and recombination (recA56 and recB21 mutants) are not more sensitive to this in vivo DNA scission, whereas strains deficient in DNA ligase (lig4 and Ug ts7 mutants) are extremely sensitive. We conclude that although DNA scission induces the SOS response, neither this induction nor recombination are required for repair. DNA ligase is necessary and may be sufficient to repair EcoRI-mediated DNA breaks in the E. coli chromosome.DNA double-strand breaks stimulate recombination in Escherichia coli and yeast (1, 2), and recombination is generally thought to repair such DNA breaks (1-3). Repair of DNA scissions has been studied previously using y-ray lesions (4); in E. coli, prior induction of the SOS DNA repair response enhances the repair of DNA cleaved by y rays (5). The SOS response is an altered physiological state that arises after DNA damage and is due to the induction of a set ofgenes, the products of which slow cell division and repair DNA (6). To repair DNA cleaved by y rays (4, 5, 7) two SOS proteins involved in recombination, RecA and RecN, and multiple copies of the genome are required, suggesting that recombination repairs these lesions. Some -ray breaks may also be repaired by ligation (8).A model for the repair of DNA scission cannot be based solely on the repair of -ray lesions, because y rays not only cleave DNA but also cause nicks and base adducts and produce free radicals that can oxidize proteins (9). In fact, single-strand nicks are 10-to 20-fold more abundant than double-strand breaks after -ray treatment (10). Furthermore, DNA scission by y rays can release a base and leave blunt termini with 5'-phosphoryl and 3'-phosphoryl or 3'-phosphoglycolate ends that cannot be ligated (11).In contrast, restriction endonucleases cleave DNA to yield staggered or blunt double-strand breaks with 3'-hydroxyl and 5'-phosphoryl termini (12). We have studied repair of staggered double-strand DNA breaks delivered with the EcoRI endonuclease, which cleaves within the DNA sequence GAATTC (13). UV sensitivity, and recN mutants were identified by mitomycin C sensitivity. Indicator medium contained 5-bromo-4-chloro-3-indolyl B3-D-galactoside (X-Gal) at 35 Ag/ml. DNA Manipulations. Plasmid pAN4, a pBR322 derivative, encodes the EcoRI restriction-modification system and ampicillin resistance (19). The EcoRI methylase gene of pAN4 was inactivated by inserting a BamHI fragment carrying the kanamycin resistance gene (20) into the Bcl I site within the methylase gene (Fig. 1). Plasmid pJC1 is a pACYC184 derivative that encodes the EcoRI methylase and chloramphenicol resistance (21). Plasmid pJH15b carries the fl intergenic region (nucleotides 5486-5941) inserted as...

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Localization of the gam gene of bacteriophage Mu and characterisation of the gene product

Cited by 26 publications

References 18 publications

Functions that protect Escherichia coli from DNA–protein crosslinks

Functions that protect Escherichia coli from DNA–protein crosslinks

Making Ends Meet: Repairing Breaks in Bacterial DNA by Non-Homologous End-Joining

Repair of the Escherichia coli chromosome after in vivo scission by the EcoRI endonuclease.

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