Cell division, guillotining of dimer chromosomes and SOS induction in resolution mutants (dif, xerC and xerD) of Escherichia coli

Hendricks, Eric; Szerlong, Heather; Hill, Thomas M.; Kuempel, Peter L.

doi:10.1046/j.1365-2958.2000.01920.x

Cited by 74 publications

(63 citation statements)

References 40 publications

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“…1; note that Miller units are corrected for cell density). The ftsK and xerD mutant strains exhibited three to five times the ␤-galactosidase activity of the wild-type strain throughout the time course, reaching a maximum of approximately 40 Miller units.…”

Section: Resultsmentioning

confidence: 97%

“…Chromosome dimer resolution (CDR) requires the XerCD recombinase, the dif site, and the FtsK cell division protein (7,8,51,102). dif, xerC, xerD, and ftsK mutants have previously been shown to be SOS constitutive (40,51,54,104), and SOS induction is blocked in these mutants if cell division is inhibited (40,54). These and other results led to a model in which unresolved dimer chromosomes are broken during cell division, thus creating the SOS-inducing signal (40).…”

Section: Fig 3 An Unstable Insertion Mutant (A)mentioning

confidence: 99%

“…dif, xerC, xerD, and ftsK mutants have previously been shown to be SOS constitutive (40,51,54,104), and SOS induction is blocked in these mutants if cell division is inhibited (40,54). These and other results led to a model in which unresolved dimer chromosomes are broken during cell division, thus creating the SOS-inducing signal (40). Indeed, Prikryl et al (86) presented direct evidence that the terminal region of the chromosome is frequently broken and degraded when CDR is blocked and that a mutation in recD can prevent the degradation.…”

Section: Fig 3 An Unstable Insertion Mutant (A)mentioning

confidence: 99%

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Isolation of SOS Constitutive Mutants ofEscherichia coli

O'Reilly

Kreuzer

2004

J Bacteriol

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The bacterial SOS regulon is strongly induced in response to DNA damage from exogenous agents such as UV radiation and nalidixic acid. However, certain mutants with defects in DNA replication, recombination, or repair exhibit a partially constitutive SOS response. These mutants presumably suffer frequent replication fork failure, or perhaps they have difficulty rescuing forks that failed due to endogenous sources of DNA damage. In an effort to understand more clearly the endogenous sources of DNA damage and the nature of replication fork failure and rescue, we undertook a systematic screen for Escherichia coli mutants that constitutively express the SOS regulon. We identified mutant strains with transposon insertions in 42 genes that caused increased expression from a dinD1::lacZ reporter construct. Most of these also displayed significant increases in basal levels of RecA protein, confirming an effect on the SOS system. As expected, this collection includes genes, such as lexA, dam, rep, xerCD, recG, and polA, which have previously been shown to cause an SOS constitutive phenotype when inactivated. The collection also includes 28 genes or open reading frames that were not previously identified as SOS constitutive, including dcd, ftsE, ftsX, purF, tdcE, and tynA. Further study of these SOS constitutive mutants should be useful in understanding the multiple causes of endogenous DNA damage. This study also provides a quantitative comparison of the extent of SOS expression caused by inactivation of many different genes in a common genetic background.Most bacteria, including Escherichia coli, elicit the SOS response following DNA damage (reviewed in references 32 and 106; see also reference 23). This response involves the transcriptional induction of a regulon with more than 30 genes, many involved in DNA damage repair, bypass, and tolerance mechanisms (e.g., recA, lexA, umuDC, polB, sulA, etc.). Expression of the SOS regulon is controlled by the RecA and LexA proteins. In the uninduced state, LexA protein represses SOS genes by binding to SOS boxes upstream of each gene (53). Following DNA damage, RecA protein becomes activated in the presence of single-stranded DNA and a nucleoside triphosphate. Activated RecA protein functions as a coprotease, mediating cleavage of LexA repressor and thus activating transcription of SOS regulon genes. As the cell recovers from the treatment, the inducing signal (single-stranded DNA) diminishes, and RecA protein returns to its unactivated state. Continued synthesis of LexA protein restores repression of the SOS genes and thereby returns the cell to the uninduced state.The SOS response is generally studied by inducing DNA damage with exogenous agents. Two of the best-studied inducers are UV irradiation and nalidixic acid. Treatment of E. coli with UV directly damages DNA by causing the formation of photoproducts, including pyrimidine dimers (32). The presence of these lesions is not sufficient to cause SOS induction, but rather the SOS inducing signal is generated when the cell att...

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Section: Resultsmentioning

confidence: 97%

Section: Fig 3 An Unstable Insertion Mutant (A)mentioning

confidence: 99%

Section: Fig 3 An Unstable Insertion Mutant (A)mentioning

confidence: 99%

See 1 more Smart Citation

Isolation of SOS Constitutive Mutants ofEscherichia coli

O'Reilly

Kreuzer

2004

J Bacteriol

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“…Crossing over by homologous recombination can lead to sister chromatid exchanges (SCEs), odd numbers of which result in dimerization of the two newly replicated chromatids when the chromosomes or replicons are circular, as is often the case in bacteria. Plasmid or chromosome dimers compromise stable plasmid inheritance and chromosome segregation (Austin et al 1981;Summers and Sherratt 1984;Blakely et al 1991;Clerget 1991;Kuempel et al 1991;Hendricks et al 2000). Hence, most bacteria with circular genomes possess the specialized Xer sitespecific recombination system to convert chromosome and plasmid circular dimers to monomers .…”

mentioning

confidence: 99%

FtsK functions in the processing of a Holliday junction intermediate during bacterial chromosome segregation

Barre¹,

Aroyo²,

Colloms³

et al. 2000

Genes Dev.

104

145

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In bacteria with circular chromosomes, homologous recombination can generate chromosome dimers that cannot be segregated to daughter cells at cell division. Xer site-specific recombination at dif, a 28-bp site located in the replication terminus region of the chromosome, converts dimers to monomers through the sequential action of the XerC and XerD recombinases. Chromosome dimer resolution requires that dif is positioned correctly in the chromosome, and the activity of FtsK, a septum-located protein that coordinates cell division with chromosome segregation. Here, we show that cycles of XerC-mediated strand exchanges form and resolve Holliday junction intermediates back to substrate irrespective of whether conditions support a complete recombination reaction. The C-terminal domain of FtsK is sufficient to activate the exchange of the second pair of strands by XerD, allowing both intra-and intermolecular recombination reactions to go to completion. Proper positioning of dif in the chromosome and of FtsK at the septum is required to sense the multimeric state of newly replicated chromosomes and restrict complete Xer reactions to dimeric chromosomes.

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“…However, such nucleoid cutting is not observed in wild-type cells, and it can be argued that in many cases where it is observed, such as mukB mutants, the structure of the nucleoid is grossly altered (30), which might suppress the inhibitory activity. Guillotining of nucleoids has also been proposed to occur in ftsK, dif, and xerCD mutants, which are unable to resolve dimeric chromosomes in a proportion of cells (11,31). It is not yet clear what allows guillotining of these dimer chromosomes.…”

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confidence: 99%

Influence of the Nucleoid on Placement of FtsZ and MinE Rings inEscherichia coli

Sun

Margolin

2001

J Bacteriol

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We previously presented evidence that replicating but unsegregated nucleoids, along with the Min system, act as topological inhibitors to restrict assembly of the FtsZ ring (Z ring) to discrete sites in the cell. To test if nonreplicating nucleoids have similar exclusion effects, we examined Z rings in dnaA (temperature sensitive) mutants. Z rings were excluded from centrally localized nucleoids and were often observed at nucleoid edges. Cells with nonreplicating nucleoids formed filaments, some of which contained large nucleoid-free areas in which Z rings were positioned at regular intervals. Because MinE may protect FtsZ from the action of the MinC inhibitor in these nucleoid-free zones, we examined the localization of a MinE-green fluorescent protein (GFP) fusion with respect to Z rings and nucleoids. Like Z rings, MinE-GFP appeared to localize independently of nucleoid position, forming rings at regular intervals in nucleoid-free regions. Unlike FtsZ, however, MinE-GFP often localized on top of nucleoids, replicating or not, suggesting that MinE is relatively insensitive to the nucleoid inhibition effect. These data suggest that both replicating and nonreplicating nucleoids are capable of topologically excluding Z rings but not MinE.Escherichia coli cells divide precisely at the midpoint of the long axis of the cell to produce two daughter cells of equal length. One of the key questions in bacterial cell biology is how the correct division plane is identified. We recently proposed a new model for division site selection in E. coli that integrated several previous hypotheses (39). One of these hypotheses, known as the nucleoid occlusion model, proposes that the nucleoid inhibits septation throughout the area of the cell that it occupies (37, 38). How might this occur? Recent evidence suggests that oriC and its associated components, such as SeqA, are centered with respect to the cell and coincide with future division sites (23,24). We propose that when these components duplicate and migrate outward from midcell during replication and segregation, they may relieve the nucleoidmediated inhibition at the vacated midcell site. The end result is that the Z ring, which is a ring structure composed of the tubulin-like protein FtsZ and is essential for initiation of septation (2,15,29), is allowed to assemble at the exact middle of the cell, followed by formation of the septum between the nucleoids.The experimental evidence for nucleoid-mediated inhibition of Z rings includes (i) the tendency of Z rings and septa to form in nucleoid-free regions in various mutants (4, 21, 39) and (ii) the failure of Z rings to assemble at the middle of parC cells, defective in topoisomerase IV, that contain a large, centrally located unsegregated nucleoid (33). Instead of assembling at midcell, Z rings in such cells usually form on the edge of the unsegregated nucleoid mass. This seems to be the default site for FtsZ assembly when the primary site at midcell is blocked.Nucleoid-mediated inhibition is only part of how division site po...

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Cell division, guillotining of dimer chromosomes and SOS induction in resolution mutants (dif, xerC and xerD) of Escherichia coli

Cited by 74 publications

References 40 publications

Isolation of SOS Constitutive Mutants ofEscherichia coli

Isolation of SOS Constitutive Mutants ofEscherichia coli

FtsK functions in the processing of a Holliday junction intermediate during bacterial chromosome segregation

Influence of the Nucleoid on Placement of FtsZ and MinE Rings inEscherichia coli

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