@article {806,
	title = {RecA4142 causes SOS constitutive expression by loading onto reversed replication forks in Escherichia coli K-12.},
	journal = {J Bacteriol},
	volume = {192},
	year = {2010},
	month = {2010 May},
	pages = {2575-82},
	abstract = {Escherichia coli initiates the SOS response when single-stranded DNA (ssDNA) produced by DNA damage is bound by RecA and forms a RecA-DNA filament. recA SOS constitutive [recA(Con)] mutants induce the SOS response in the absence of DNA damage. It has been proposed that recA(Con) mutants bind to ssDNA at replication forks, although the specific mechanism is unknown. Previously, it had been shown that recA4142(F217Y), a novel recA(Con) mutant, was dependent on RecBCD for its high SOS constitutive [SOS(Con)] expression. This was presumably because RecA4142 was loaded at a double-strand end (DSE) of DNA. Herein, it is shown that recA4142 SOS(Con) expression is additionally dependent on ruvAB (replication fork reversal [RFR] activity only) and recJ (5{\textquoteright}-->3{\textquoteright} exonuclease), xonA (3{\textquoteright}-->5{\textquoteright} exonuclease) and partially dependent on recQ (helicase). Lastly, sbcCD mutations (Mre11/Rad50 homolog) in recA4142 strains caused full SOS(Con) expression in an ruvAB-, recBCD-, recJ-, and xonA-independent manner. It is hypothesized that RuvAB catalyzes RFR, RecJ and XonA blunt the DSE (created by the RFR), and then RecBCD loads RecA4142 onto this end to produce SOS(Con) expression. In sbcCD mutants, RecA4142 can bind other DNA substrates by itself that are normally degraded by the SbcCD nuclease.},
	keywords = {Bacterial Proteins, Deoxyribonucleases, DNA Helicases, DNA Replication, Endodeoxyribonucleases, Escherichia coli K12, Escherichia coli Proteins, Exodeoxyribonuclease V, Exodeoxyribonucleases, Exonucleases, Microscopy, Fluorescence, Mutation, Rec A Recombinases, SOS Response (Genetics)},
	issn = {1098-5530},
	doi = {10.1128/JB.01623-09},
	author = {Long, Jarukit Edward and Massoni, Shawn C and Sandler, Steven J}
}
@article {811,
	title = {UvrD303, a hyperhelicase mutant that antagonizes RecA-dependent SOS expression by a mechanism that depends on its C terminus.},
	journal = {J Bacteriol},
	volume = {191},
	year = {2009},
	month = {2009 Mar},
	pages = {1429-38},
	abstract = {Genomic integrity is critical for an organism{\textquoteright}s survival and ability to reproduce. In Escherichia coli, the UvrD helicase has roles in nucleotide excision repair and methyl-directed mismatch repair and can limit reactions by RecA under certain circumstances. UvrD303 (D403A D404A) is a hyperhelicase mutant, and when expressed from a multicopy plasmid, it results in UV sensitivity (UV(s)), recombination deficiency, and antimutability. In order to understand the molecular mechanism underlying the UV(s) phenotype of uvrD303 cells, this mutation was transferred to the E. coli chromosome and studied in single copy. It is shown here that uvrD303 mutants are UV sensitive, recombination deficient, and antimutable and additionally have a moderate defect in inducing the SOS response after UV treatment. The UV-sensitive phenotype is epistatic with recA and additive with uvrA and is partially suppressed by removing the LexA repressor. Furthermore, uvrD303 is able to inhibit constitutive SOS expression caused by the recA730 mutation. The ability of UvrD303 to antagonize SOS expression was dependent on its 40 C-terminal amino acids. It is proposed that UvrD303, via its C terminus, can decrease the levels of RecA activity in the cell.},
	keywords = {DNA Helicases, DNA, Bacterial, Escherichia coli K12, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Mutation, Rec A Recombinases, Recombination, Genetic, SOS Response (Genetics), Ultraviolet Rays},
	issn = {1098-5530},
	doi = {10.1128/JB.01415-08},
	author = {Centore, Richard C and Leeson, Michael C and Sandler, Steven J}
}
@article {810,
	title = {Differential requirements of two recA mutants for constitutive SOS expression in Escherichia coli K-12.},
	journal = {PLoS One},
	volume = {3},
	year = {2008},
	month = {2008},
	pages = {e4100},
	abstract = {BACKGROUND: Repairing DNA damage begins with its detection and is often followed by elicitation of a cellular response. In E. coli, RecA polymerizes on ssDNA produced after DNA damage and induces the SOS Response. The RecA-DNA filament is an allosteric effector of LexA auto-proteolysis. LexA is the repressor of the SOS Response. Not all RecA-DNA filaments, however, lead to an SOS Response. Certain recA mutants express the SOS Response (recA(C)) in the absence of external DNA damage in log phase cells.

METHODOLOGY/PRINCIPAL FINDINGS: Genetic analysis of two recA(C) mutants was used to determine the mechanism of constitutive SOS (SOS(C)) expression in a population of log phase cells using fluorescence of single cells carrying an SOS reporter system (sulAp-gfp). SOS(C) expression in recA4142 mutants was dependent on its initial level of transcription, recBCD, recFOR, recX, dinI, xthA and the type of medium in which the cells were grown. SOS(C) expression in recA730 mutants was affected by none of the mutations or conditions tested above.

CONCLUSIONS/SIGNIFICANCE: It is concluded that not all recA(C) alleles cause SOS(C) expression by the same mechanism. It is hypothesized that RecA4142 is loaded on to a double-strand end of DNA and that the RecA filament is stabilized by the presence of DinI and destabilized by RecX. RecFOR regulate the activity of RecX to destabilize the RecA filament. RecA730 causes SOS(C) expression by binding to ssDNA in a mechanism yet to be determined.},
	keywords = {Escherichia coli K12, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Genes, Bacterial, Models, Biological, Mutation, Rec A Recombinases, SOS Response (Genetics)},
	issn = {1932-6203},
	doi = {10.1371/journal.pone.0004100},
	author = {Long, Jarukit Edward and Renzette, Nicholas and Centore, Richard C and Sandler, Steven J}
}
@article {814,
	title = {XthA (Exonuclease III) regulates loading of RecA onto DNA substrates in log phase Escherichia coli cells.},
	journal = {Mol Microbiol},
	volume = {67},
	year = {2008},
	month = {2008 Jan},
	pages = {88-101},
	abstract = {Exonucleases can modify DNA substrates created during DNA replication, recombination and repair. In Escherichia coli, the effects of several 3{\textquoteright}-5{\textquoteright} exonucleases on RecA loading were studied by assaying RecA-GFP foci formation. Mutations in xthA (ExoIII), xseAB (ExoVII), xni (ExoIX), exoX (ExoX) and tatD (ExoXI) increased the number of RecA-GFP foci twofold to threefold in a population of log phase cells grown in minimal medium. These increases depend on xonA. Epistasis analysis shows that ExoVII, ExoX, ExoIX and ExoXI function in a common pathway, distinct from ExoIII (and ExoI is upstream of both pathways). It is shown (paradoxically) that in xthA mutants, RecA-GFP loading is predominantly RecBCD-dependent and that xthA recB double mutants are viable. Experiments show that while log phase xthA cells have twofold more double-stranded breaks (DSBs) than wild type, they do not induce the SOS response. The increase in RecA loading is independent of the base excision repair (BER) proteins Nth, MutM and Nei. It is proposed that log phase cells produce DSBs that do not induce the SOS response. Furthermore, ExoI, ExoIII and the other 3{\textquoteright}-5{\textquoteright} exonucleases process these DSBs, antagonizing the RecBCD pathway of RecA loading, thus regulating the availability of these substrates for recombination.},
	keywords = {DNA Breaks, Double-Stranded, DNA Repair, DNA, Bacterial, Epistasis, Genetic, Escherichia coli K12, Escherichia coli Proteins, Exodeoxyribonucleases, Green Fluorescent Proteins, Microbial Viability, Rec A Recombinases, Recombinant Fusion Proteins, SOS Response (Genetics)},
	issn = {0950-382X},
	doi = {10.1111/j.1365-2958.2007.06026.x},
	author = {Centore, Richard C and Lestini, Roxane and Sandler, Steven J}
}
@article {817,
	title = {UvrD limits the number and intensities of RecA-green fluorescent protein structures in Escherichia coli K-12.},
	journal = {J Bacteriol},
	volume = {189},
	year = {2007},
	month = {2007 Apr},
	pages = {2915-20},
	abstract = {RecA is important for recombination, DNA repair, and SOS induction. In Escherichia coli, RecBCD, RecFOR, and RecJQ prepare DNA substrates onto which RecA binds. UvrD is a 3{\textquoteright}-to-5{\textquoteright} helicase that participates in methyl-directed mismatch repair and nucleotide excision repair. uvrD deletion mutants are sensitive to UV irradiation, hypermutable, and hyper-rec. In vitro, UvrD can dissociate RecA from single-stranded DNA. Other experiments suggest that UvrD removes RecA from DNA where it promotes unproductive reactions. To test if UvrD limits the number and/or the size of RecA-DNA structures in vivo, an uvrD mutation was combined with recA-gfp. This recA allele allows the number of RecA structures and the amount of RecA at these structures to be assayed in living cells. uvrD mutants show a threefold increase in the number of RecA-GFP foci, and these foci are, on average, nearly twofold higher in relative intensity. The increased number of RecA-green fluorescent protein foci in the uvrD mutant is dependent on recF, recO, recR, recJ, and recQ. The increase in average relative intensity is dependent on recO and recQ. These data support an in vivo role for UvrD in removing RecA from the DNA.},
	keywords = {DNA Helicases, DNA, Bacterial, DNA-Binding Proteins, Escherichia coli K12, Escherichia coli Proteins, Green Fluorescent Proteins, Molecular Sequence Data, Mutagenesis, Rec A Recombinases, Recombinant Fusion Proteins},
	issn = {0021-9193},
	doi = {10.1128/JB.01777-06},
	author = {Centore, Richard C and Sandler, Steven J}
}
@article {822,
	title = {Allele specific synthetic lethality between priC and dnaAts alleles at the permissive temperature of 30 degrees C in E. coli K-12.},
	journal = {BMC Microbiol},
	volume = {4},
	year = {2004},
	month = {2004},
	pages = {47},
	abstract = {BACKGROUND: DnaA is an essential protein in the regulation and initiation of DNA replication in many bacteria. It forms a protein-DNA complex at oriC to which DnaC loads DnaB. DNA replication forks initiated at oriC by DnaA can collapse on route to the terminus for a variety of reasons. PriA, PriB, PriC, DnaT, Rep and DnaC form multiple pathways to restart repaired replication forks. DnaC809 and dnaC809,820 are suppressors of priA2::kan mutant phenotypes. The former requires PriC and Rep while the latter is independent of them. RnhA339::cat mutations allow DnaA-independent initiation of DNA replication.

RESULTS: It is shown herein that a priC303::kan mutation is synthetically lethal with either a dnaA46 or dnaA508 temperature sensitive mutation at the permissive temperature of 30 degrees C. The priC-dnaA lethality is specific for the dnaA allele. The priC303::kan mutant was viable when placed in combination with either dnaA5, dnaA167, dnaA204 or dnaA602. The priC-dnaA508 and priC-dnaA46 lethality could be suppressed by rnhA339::cat. The priC-dnaA508 lethality could be suppressed by a dnaC809,820 mutation, but not dnaC809. Neither of the dnaC mutations could suppress the priC-dnaA46 lethality.

CONCLUSIONS: A hitherto unknown function for either DnaA in replication restart or PriC in initiation of DNA replication that occurs in certain dnaA temperature sensitive mutant strains at the permissive temperature of 30 degrees C has been documented. Models considering roles for PriC during initiation of DNA replication and roles for DnaA in replication restart were tested and found not to decisively explain the data. Other roles of dnaA in transcription and nucleoid structure are additionally considered.},
	keywords = {Alleles, Bacterial Proteins, DNA Replication, DNA-Binding Proteins, Escherichia coli K12, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Genes, Lethal, Mutation, Temperature},
	issn = {1471-2180},
	doi = {10.1186/1471-2180-4-47},
	author = {Hinds, Tania and Sandler, Steven J}
}
@article {824,
	title = {A dnaT mutant with phenotypes similar to those of a priA2::kan mutant in Escherichia coli K-12.},
	journal = {Genetics},
	volume = {167},
	year = {2004},
	month = {2004 Jun},
	pages = {569-78},
	abstract = {The ability to repair damaged replication forks and restart them is important for cell survival. DnaT is essential for replication restart in vitro and yet no definite genetic analysis has been done in Escherichia coli K-12. To begin, dnaT822, an in-frame six-codon (87-92) deletion was constructed. DnaT822 mutants show colony size, cell morphology, inability to properly partition nucleoids, UV sensitivity, and basal SOS expression similar to priA2::kan mutants. DnaT822 priA2::kan double mutants had phenotypes similar to those of the single mutants. DnaT822 and dnaT822 priA2::kan mutant phenotypes were fully suppressed by dnaC809. Previously, a dominant temperature-sensitive lethal mutation, dnaT1, had been isolated in E. coli 15T(-). DnaT1 was found to have a base-pair change relative to the E. coli 15T(-) and E. coli K-12 dnaT genes that led to a single amino acid change: R152C. A plasmid-encoded E. coli K-12 mutant dnaT gene with the R152C amino acid substitution did not display a dominant temperature-sensitive lethal phenotype in a dnaT(+) strain of E. coli K-12. Instead, this mutant dnaT gene was found to complement the E. coli K-12 dnaT822 mutant phenotypes. The significance of these results is discussed in terms of models for replication restart.},
	keywords = {Base Sequence, Codon, DNA Primers, DNA Repair, DNA Replication, DNA, Bacterial, DNA-Binding Proteins, Escherichia coli K12, Escherichia coli Proteins, Molecular Sequence Data, Mutation, Plasmids, Polymerase Chain Reaction, Sequence Deletion},
	issn = {0016-6731},
	doi = {10.1534/genetics.103.025296},
	author = {McCool, Jesse D and Ford, Christopher C and Sandler, Steven J}
}
@article {823,
	title = {Measurement of SOS expression in individual Escherichia coli K-12 cells using fluorescence microscopy.},
	journal = {Mol Microbiol},
	volume = {53},
	year = {2004},
	month = {2004 Sep},
	pages = {1343-57},
	abstract = {Many recombination, DNA repair and DNA replication mutants have high basal levels of SOS expression as determined by a sulAp-lacZ reporter gene system on a population of cells. Two opposing models to explain how the SOS expression is distributed in these cells are: (i) the {\textquoteright}Uniform Expression Model (UEM){\textquoteright} where expression is evenly distributed in all cells or (ii) the {\textquoteright}Two Population Model (TPM){\textquoteright} where some cells are highly induced while others are not at all. To distinguish between these two models, a method to quantify SOS expression in individual bacterial cells was developed by fusing an SOS promoter (sulAp) to the green fluorescent protein (gfp) reporter gene and inserting it at attlambda on the Escherichia coli chromosome. It is shown that the fluorescence in sulAp-gfp cells is regulated by RecA and LexA. This system was then used to distinguish between the two models for several mutants. The patterns displayed by priA, dnaT, recG, uvrD, dam, ftsK, rnhA, polA and xerC mutants were explained best by the TPM while only lexA (def), lexA3 (ind-) and recA defective mutants were explained best by the UEM. These results are discussed in a context of how the processes of DNA replication and recombination may affect cells in a population differentially.},
	keywords = {Adenosine Triphosphatases, DNA Damage, DNA Helicases, DNA Repair, Escherichia coli K12, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Genes, Reporter, Microscopy, Fluorescence, Models, Genetic, Promoter Regions, Genetic, Recombinant Fusion Proteins, SOS Response (Genetics), Ultraviolet Rays},
	issn = {0950-382X},
	doi = {10.1111/j.1365-2958.2004.04225.x},
	author = {McCool, Jesse D and Long, Edward and Petrosino, Joseph F and Sandler, Hilary A and Rosenberg, Susan M and Sandler, Steven J}
}
