Expansion of CTG repeats from human disease genes is dependent upon replication mechanisms in Escherichia coli: the effect of long patch mismatch repair revisited

Schumacher, Sylvie; Fuchs, Robert P. P.; Bichara, Marc

doi:10.1006/jmbi.1998.1827

Cited by 57 publications

(44 citation statements)

References 27 publications

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“…A number of studies have documented the stabilizing and destabilizing effects of MutS and its homologs on CAGÁCTG repeat instability in E. coli, yeast, and mouse Schumacher et al 1998;Manley et al 1999;Schmidt et al 2000). In this system, we observe a small destabilizing effect of the mutS mutation in one orientation (CAG on leading-strand template) that lies on the border of significance and no significant effect in the other orientation (CTG on leading-strand template).…”

Section: Transcription Does Not Affect Cagáctg Repeat Instabilitymentioning

confidence: 71%

Proofreading and Secondary Structure Processing Determine the Orientation Dependence of CAG·CTG Trinucleotide Repeat Instability inEscherichia coli

et al. 2007

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Expanded CAGÁCTG trinucleotide repeat tracts are associated with several human inherited diseases, including Huntington's disease, myotonic dystrophy, and spinocerebellar ataxias. Here we describe a new model system to investigate repeat instability in the Escherichia coli chromosome. Using this system, we reveal patterns of deletion instability consistent with secondary structure formation in vivo and address the molecular basis of orientation-dependent instability. We demonstrate that the orientation dependence of CAGÁCTG trinucleotide repeat deletion is determined by the proofreading subunit of DNA polymerase III (DnaQ) in the presence of the hairpin nuclease SbcCD (Rad50/Mre11). Our results suggest that, although initiation of slippage can occur independently of CAGÁCTG orientation, the folding of the intermediate affects its processing and this results in orientation dependence. We propose that proofreading is inefficient on the CTG-containing strand because of its ability to misfold and that SbcCD contributes to processing in a manner that is dependent on proofreading and repeat tract orientation. Furthermore, we demonstrate that transcription and recombination do not influence instability in this system.

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Section: Transcription Does Not Affect Cagáctg Repeat Instabilitymentioning

confidence: 71%

Proofreading and Secondary Structure Processing Determine the Orientation Dependence of CAG·CTG Trinucleotide Repeat Instability inEscherichia coli

et al. 2007

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“…2, A and B). Because plasmids harboring TNR sequences of intermediate lengths have no selective growth advantage in bacteria (38), the effects of transcription could be cleanly resolved from those induced by replication. Each plasmid was transformed into BL21(DE3pLysE) bacteria that contain an IPTG-inducible T7 RNA polymerase under the control of the lac repressor ( Fig.…”

Section: Orientation Dependence Of Tnr Instability Cannot Be Distingumentioning

confidence: 99%

Single-stranded DNA-binding Protein in Vitro Eliminates the Orientation-dependent Impediment to Polymerase Passage on CAG/CTG Repeats

Delagoutte

Goellner

Guo

et al. 2008

Journal of Biological Chemistry

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Small insertions and deletions of trinucleotide repeats (TNRs) can occur by polymerase slippage and hairpin formation on either template or newly synthesized strands during replication. Although not predicted by a slippage model, deletions occur preferentially when 5-CTG is in the lagging strand template and are highly favored over insertion events in rapidly replicating cells. The mechanism for the deletion bias and the orientation dependence of TNR instability is poorly understood. We report here that there is an orientation-dependent impediment to polymerase progression on 5-CAG and 5-CTG repeats that can be relieved by the binding of single-stranded DNAbinding protein. The block depends on the primary sequence of the TNR but does not correlate with the thermodynamic stability of hairpins. The orientation-dependent block of polymerase passage is the strongest when 5-CAG is the template. We propose a "template-push" model in which the slow speed of DNA polymerase across the 5-CAG leading strand template creates a threat to helicase-polymerase coupling. To prevent uncoupling, the TNR template is pushed out and by-passed. Hairpins do not cause the block, but appear to occur as a consequence of polymerase pass-over. Expansion of simple trinucleotide repeats (TNRs)4 is the underlying genetic defect of a number of human neurodegenerative diseases. TNR-associated pathophysiology in human diseases strictly depends on the number of trinucleotide repeats (reviewed in Refs. 1-3). Although expansion can occur in germ cells (4) and in somatic cells with age (5, 6), emerging evidence suggests that rapid cell division in the early embryo can reduce the size of the repeats and modulate disease potential (7). TNR deletion during rapid cell division may serve as a natural defense mechanism for keeping the length of the repeats in check at critical times in development. Reducing the length of the repeat tract in disease genes is being explored as a therapeutic strategy. However, the mechanisms by which deletions rather than expansions are favored during replication remain poorly understood.DNA polymerase and strand slippage has been proposed as the primary mechanism for instability of trinucleotide repeats (1-3). During replication, the TNR units can misalign resulting in an extrahelical DNA loop that increases TNR length if it occurs on the daughter strand and decreases TNR length if it occurs on the template strand (1-3). In both prokaryotic and eukaryotic models, it is well established that TNR instability is sensitive to the length of the repeat (8 -12), to its structure forming potential (13-17), and to its proximity to the origin of replication (18). The factors that regulate the probability and frequency of deletion events, however, remain poorly understood. By a polymerase slippage model, a deletion implies that hairpin formation has occurred on the template strand. Theoretically, for an identical sequence located either on the template or daughter strand, slippage and hairpin formation can occur with equivalent frequen...

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“…Furthermore, polymerase switching (PolI/PolIII) has been implicated in E. coli to contribute to the genetic instability of triplet repeats (16,47). Polymerase switching has also been proposed to occur during eukaryotic replication where following synthesis of the RNA-DNA primer by the polymerase ␣-primase complex, replication is continued by polymerase ␦, both on the leading and lagging strands (87,119).…”

Section: Chemical Probe Determinations-d(cagg)mentioning

confidence: 99%

Hairpin Structure-forming Propensity of the (CCTG·CAGG) Tetranucleotide Repeats Contributes to the Genetic Instability Associated with Myotonic Dystrophy Type 2

Dere

Напиерала

Ranum

et al. 2004

Journal of Biological Chemistry

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The genetic instabilities of (CCTG⅐CAGG) n tetranucleotide repeats were investigated to evaluate the molecular mechanisms responsible for the massive expansions found in myotonic dystrophy type 2 (DM2) patients. DM2 is caused by an expansion of the repeat from the normal allele of 26 to as many as 11,000 repeats. Genetic expansions and deletions were monitored in an African green monkey kidney cell culture system (COS-7 cells) as a function of the length (30, 114, or 200 repeats), orientation, or proximity of the repeat tracts to the origin (SV40) of replication. As found for CTG⅐CAG repeats related to DM1, the instabilities were greater for the longer tetranucleotide repeat tracts. Also, the expansions and deletions predominated when cloned in orientation II (CAGG on the leading strand template) rather than I and when cloned proximal rather than distal to the replication origin. Biochemical studies on synthetic d(CAGG) 26 and d(CCTG) 26 as models of unpaired regions of the replication fork revealed that d(CAGG) 26 has a marked propensity to adopt a defined base paired hairpin structure, whereas the complementary d(CCTG) 26 lacks this capacity. The effect of orientation described above differs from all previous results with three triplet repeat sequences (including CTG⅐CAG), which are also involved in the etiologies of other hereditary neurological diseases. However, similar to the triplet repeat sequences, the ability of one of the two strands to form a more stable folded structure, in our case the CAGG strand, explains this unorthodox "reversed" behavior.

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Expansion of CTG repeats from human disease genes is dependent upon replication mechanisms in Escherichia coli: the effect of long patch mismatch repair revisited

Cited by 57 publications

References 27 publications

Proofreading and Secondary Structure Processing Determine the Orientation Dependence of CAG·CTG Trinucleotide Repeat Instability inEscherichia coli

Proofreading and Secondary Structure Processing Determine the Orientation Dependence of CAG·CTG Trinucleotide Repeat Instability inEscherichia coli

Single-stranded DNA-binding Protein in Vitro Eliminates the Orientation-dependent Impediment to Polymerase Passage on CAG/CTG Repeats

Hairpin Structure-forming Propensity of the (CCTG·CAGG) Tetranucleotide Repeats Contributes to the Genetic Instability Associated with Myotonic Dystrophy Type 2

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