Error-prone SOS repair can be error-free

Liu, Shi-Kau; Tessman, Irwin

doi:10.1016/s0022-2836(99)80001-1

Cited by 17 publications

(5 citation statements)

References 19 publications

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“…Liu and Tessman have reported that groE mutations may have a greater effect on mutagenesis than they do on repair. The interactions between UmuC and GroEL and GroES, in addition to affecting the stability of UmuC, may alter its activity to promote mutagenic repair (17,18).…”

Section: Discussionmentioning

confidence: 99%

Coexpression of UmuD' with UmuC suppresses the UV mutagenesis deficiency of groE mutants

Donnelly

Walker

1992

J Bacteriol

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The GroE proteins of Escherichia coli are heat shock proteins which have also been shown to be molecular chaperone proteins. Our previous work has shown that the GroE proteins of E. coli are required for UV mutagenesis. This process requires the umuDC genes which are regulated by the SOS regulon. As part of the UV mutagenesis pathway, the product of the umuD gene, UmuD, is posttranslationally cleaved to yield the active form, UmuD'. In order to investigate what role the groE gene products play in UV mutagenesis, we measured UV mutagenesis in groE+ and groE strains which were expressing either the umuDC or umuD'C genes. We found that expression of umuD' instead of umuD will suppress the nonmutability conferred by the groE mutations. However, cleavage of UmuD to UmuD' is unaffected by mutations at the groE locus. Instead we found that the presence of UmuD' increased the stability of UmuC in groE strains. In addition, we obtained evidence which indicates that GroEL interacts directly with UmuC.

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Section: Discussionmentioning

confidence: 99%

Coexpression of UmuD' with UmuC suppresses the UV mutagenesis deficiency of groE mutants

Donnelly

Walker

1992

J Bacteriol

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“…It is notable, therefore, that under SOS conditions the cell deliberately imposes what seems at first glance to be an unnecessary delay in repair. One way to view this delay is to see it as part of a strategy to increase the mutation frequency when the cell is subjected to adverse environmental conditions to which it must adapt (7,31,32).…”

Section: Discussionmentioning

confidence: 99%

“…This paradox will be resolved by the fact that mutations can arise by deamination of cytosine in cyclobutane dimers; if the uracils formed are read correctly during bypass of the dimers, adenines would be found in the newly synthesized complementary strand. If there is adequate time for deamination to occur, and that is the very central issue here, bypass of lesions will usually involve the insertion of the sequence A-A opposite cyclobutane dimers, even opposite those dimers that had originally contained C. Because of the distorted template, partially relaxed proofreading might be needed to facilitate the accurate bypass (6,7).…”

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confidence: 99%

Mechanism of SOS mutagenesis of UV-irradiated DNA: mostly error-free processing of deaminated cytosine.

Tessman

Liu

Kennedy

1992

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

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We measured the kinetics of growth and mutagenesis of UV-irradiated DNA of phages S13 and A that were undergoing SOS repair; the kinetics strongly suggest that most of SOS mutagenesis arises from the deamination of cytosine in cyclobutane pyrimidine dimers, producing C -3 T transitions. This occurs because the SOS mechanism bypasses T'T dimers promptly, while bypass of cytosine-containing dimers is delayed long enough for deamination to occur. The mutations are thus primarily the product of a faithful mechanism of lesion bypass by a DNA polymerase and are not, as had been generally thought, the product of an error-prone mechanism. All of these observations are explained by the A-rule, which is that adenine nucleotides are inserted noninstructionally opposite DNA lesions.SOS repair and SOS mutagenesis were discovered nearly 40 years ago by Jean Weigle, who observed that preirradiation of the bacterial host increased survival of UV-irradiated phage A (1). When applied to phage DNA these SOS phenomena are now called Weigle reactivation and Weigle mutagenesis; their mechanism has thus been an intriguing puzzle for some time. We show here that the primary, but not the sole, mechanism of UV mutagenesis in phages S13 and A is simply the spontaneous deamination of cytosine in cyclobutane pyrimidine dimers. This deamination occurs during a deliberate, and arguably an unnecessary, delay in the bypass of the lesion by DNA polymerase; the delay is caused by cytosine-containing dimers, possibly because of the mispairing of the cytosine with adenine. SOS repair is induced by damage to DNA. In Escherichia coli, the damage results in an activated form of the RecA protein, which can mediate the cleavage of LexA, the repressor ofthe SOS regulon. The principal known components of the repair system are the products of the recA and the umuDC genes. The activated RecA protein is needed for cleavage of the UmuD protein to produce UmuD', the active C-terminal fragment (2-4). The RecA protein can also be activated by mutations designated recA(Prtc) to what is termed the protease constitutive state (5); with mutants such as recAl202(Prtc) and recAJ237(Prtc), which were used in the work described here, Weigle reactivation is achieved without irradiation of the host cell.It is generally thought that a high frequency of erroneous base pairing during DNA synthesis opposite the distorted lesion is responsible for the mutagenesis that accompanies SOS repair, and that idea has evoked the term error-prone repair. We propose, instead, that most, though certainly not all, ofthe mutations arise through accurate base pairing-i.e., an error-free bypass mechanism. This paradox will be resolved by the fact that mutations can arise by deamination of cytosine in cyclobutane dimers; if the uracils formed are read correctly during bypass of the dimers, adenines would be found in the newly synthesized complementary strand. If there is adequate time for deamination to occur, and that is the very central issue here, bypass of lesions will usually invo...

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“…Taken together, RecA and Pol V collaborate to form a complex capable of lesion bypass. Finally, the molecular chaperones GroES and GroEL are required for Pol V dependent UV induced mutagenesis possibly functioning to help stabilize UmuC by facilitating correct folding (94, 95, 220). Consistent with this conclusion, the half-life of UmuC decreases in groE strains (95).…”

Section: Sos Mutagenesismentioning

confidence: 99%

The SOS Regulatory Network

et al. 2008

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All organisms possess a diverse set of genetic programs that are used to alter cellular physiology in response to environmental cues. The gram-negative bacterium, Escherichia coli, mounts what is known as the “SOS response” following DNA damage, replication fork arrest, and a myriad of other environmental stresses. For over 50 years, E. coli has served as the paradigm for our understanding of the transcriptional, and physiological changes that occur following DNA damage (400). In this chapter, we summarize the current view of the SOS response and discuss how this genetic circuit is regulated. In addition to examining the E. coli SOS response, we also include a discussion of the SOS regulatory networks in other bacteria to provide a broader perspective on how prokaryotes respond to DNA damage.

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Error-prone SOS repair can be error-free

Cited by 17 publications

References 19 publications

Coexpression of UmuD' with UmuC suppresses the UV mutagenesis deficiency of groE mutants

Coexpression of UmuD' with UmuC suppresses the UV mutagenesis deficiency of groE mutants

Mechanism of SOS mutagenesis of UV-irradiated DNA: mostly error-free processing of deaminated cytosine.

The SOS Regulatory Network

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