Interactions between the Werner Syndrome Helicase and DNA Polymerase δ Specifically Facilitate Copying of Tetraplex and Hairpin Structures of the d(CGG) Trinucleotide Repeat Sequence

Abstract

Werner syndrome (WS) is an inherited disorder characterized by premature aging and genomic instability. The protein encoded by the WS gene, WRN, possesses intrinsic 3′ → 5′ DNA helicase and 3′ → 5′ DNA exonuclease activities. WRN helicase resolves alternate DNA structures including tetraplex and triplex DNA, and Holliday junctions. Thus, one function of WRN may be to unwind secondary structures that impede cellular DNA transactions. We report here that hairpin and G′2 bimolecular tetraplex structures of the fragile X expanded sequence, d(CGG)n, effectively impede synthesis by three eukaryotic replicative DNA polymerases (pol): pol α, pol δ, and pol ε. The constraints imposed on pol δ-catalyzed synthesis are relieved, however, by WRN; WRN facilitates pol δ to traverse these template secondary structures to synthesize full-length DNA products. The alleviatory effect of WRN is limited to pol δ; neither pol α nor pol ε can traverse template d(CGG)n hairpin and tetraplex structures in the presence of WRN. Alleviation of pausing by pol δ is observed with Escherichia coli RecQ but not with UvrD helicase, suggesting a concerted action of RecQ helicases and pol δ. Our findings suggest a possible role of WRN in rescuing pol δ-mediated replication at forks stalled by unusual DNA secondary structures. Werner syndrome (WS) is an inherited disorder characterized by premature aging and genomic instability. The protein encoded by the WS gene, WRN, possesses intrinsic 3′ → 5′ DNA helicase and 3′ → 5′ DNA exonuclease activities. WRN helicase resolves alternate DNA structures including tetraplex and triplex DNA, and Holliday junctions. Thus, one function of WRN may be to unwind secondary structures that impede cellular DNA transactions. We report here that hairpin and G′2 bimolecular tetraplex structures of the fragile X expanded sequence, d(CGG)n, effectively impede synthesis by three eukaryotic replicative DNA polymerases (pol): pol α, pol δ, and pol ε. The constraints imposed on pol δ-catalyzed synthesis are relieved, however, by WRN; WRN facilitates pol δ to traverse these template secondary structures to synthesize full-length DNA products. The alleviatory effect of WRN is limited to pol δ; neither pol α nor pol ε can traverse template d(CGG)n hairpin and tetraplex structures in the presence of WRN. Alleviation of pausing by pol δ is observed with Escherichia coli RecQ but not with UvrD helicase, suggesting a concerted action of RecQ helicases and pol δ. Our findings suggest a possible role of WRN in rescuing pol δ-mediated replication at forks stalled by unusual DNA secondary structures. Werner syndrome Werner syndrome protein DNA polymerase δ DNA polymerase α DNA polymerase ε nucleotide(s) Werner Syndrome (WS),1characterized by premature aging and genomic instability (1Epstein C.J. Martin G.M. Schultz A.L. Motulsky A.G. Medicine. 1966; 45: 177-221Crossref PubMed Scopus (735) Google is a of in the WS The encoded by the WS gene, WRN, a by DNA helicases of the RecQ Martin G.M. PubMed Scopus Google of DNA helicases is by Escherichia coli RecQ PubMed Scopus Google PubMed Google PubMed Scopus Google PubMed Scopus Google and PubMed Google PubMed Scopus Google and and PubMed Scopus Google RecQ DNA helicases in Google PubMed Scopus Google WRN is of the RecQ helicase in that an exonuclease PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google WRN protein to in to an 3′ → 5′ DNA helicase an intrinsic 3′ → 5′ DNA exonuclease PubMed Scopus Google PubMed Scopus Google helicase of DNA a 3′ DNA a helicase DNA Martin G.M. PubMed Scopus Google PubMed Scopus Google WRN that the is of in The of WRN can be by the replication protein PubMed Scopus Google in WRN DNA PubMed Scopus Google WRN can unwind alternate DNA including DNA PubMed Scopus Google Holliday PubMed Scopus Google and triplex DNA PubMed Scopus Google of WRN and in The of WS PubMed Scopus Google PubMed Scopus Google to the PubMed Scopus Google and the of a and WRN and the replicative DNA pol δ PubMed Scopus Google Scopus Google the that WRN is in of DNA is the a function of WRN helicase may be to alternate DNA structures of the replication that impede the of DNA to the function of the helicase in PubMed Google DNA tetraplex structures in PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google of DNA are by that are by and by the of tetraplex DNA structures in is by DNA and the to on in PubMed Scopus Google and in PubMed Scopus Google PubMed Scopus Google in is the of hairpin PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and tetraplex structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google by the in to fragile X and tetraplex structures of to of DNA polymerases in DNA synthesis PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google of replicative DNA polymerases in polymerase and of the report that DNA synthesis by eukaryotic DNA polymerases is by hairpin and bimolecular G′2 tetraplex structures of a in template of WRN helicase, however, pol δ to traverse these template secondary structures and to synthesize full-length that the of WRN to polymerase at these secondary structures is and limited to pol and and and by by WRN protein to by the by PubMed Scopus Google of WRN protein a of WRN on a RecQ helicase by of and UvrD helicase a DNA pol δ and pol to PubMed Scopus Google of pol δ and pol DNA polymerase and DNA polymerase ε the of and of of with by and to the the by the DNA with template by a with an of template DNA in The at and the to by to in to template DNA in an The with to a DNA of in the presence of in a of The at to of tetraplex the of to by the of of the DNA in of a in The at at a of to tetraplex of the and tetraplex DNA by and the The in and at of by the DNA with and in of the DNA at of the tetraplex DNA the of of to a of The hairpin template in DNA template by of DNA polymerases in the presence of of DNA DNA synthesis in that in a of and of and the of template not at the by on and of The and The and by by in that in of the tetraplex DNA with of coli coli UvrD at The by the of of a and and of tetraplex DNA by of a in at a of by PubMed Scopus Google DNA that WRN in are not of to in DNA WS including a of DNA and a of PubMed Scopus Google PubMed Scopus Google these are to the PubMed Scopus Google The and of WRN with a replicative DNA pol δ PubMed Scopus Google Scopus Google a role of WRN in the that of pol δ by WRN in the of the pol δ Scopus Google that WRN may not in DNA with the that WRN can unwind alternate DNA structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google to that WRN may be in replication at forks by DNA stalled by DNA secondary structures. report in by the effect of WRN on the of synthesis by pol δ hairpin and tetraplex DNA bimolecular tetraplex hairpin of the d(CGG)n template secondary structures. in the of PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google The of d(CGG)n to PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and to structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google in the of that to fragile X and tetraplex structures of d(CGG)n to the of DNA polymerases in PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and in G.M. PubMed Scopus Google a DNA template that a hairpin a bimolecular G′2 tetraplex in the presence of with that the template G′2 hairpin and tetraplex structures a to DNA synthesis by three eukaryotic replicative DNA α, δ, and ε and of a by three DNA polymerases the of the with DNA the of polymerase is that of the is the DNA the of the tetraplex not of WRN pausing by pol δ at the tetraplex a of the full-length DNA of that of pol δ pausing is a of the tetraplex d(CGG)n of WRN. WRN is to unwind the template G′2 tetraplex in the presence of in not is with that can in PubMed Scopus Google the helicase WRN protein that is to unwind DNA PubMed Scopus Google Martin G.M. PubMed Scopus Google to of pol δ by the of of WRN and pol δ, that of polymerase pausing that of the tetraplex synthesis with DNA synthesis by pol δ to synthesis the G′2 tetraplex replicative and to full-length DNA in the presence of WRN by to be limited to pol δ. WRN not pol α the pol δ pol to traverse the template tetraplex and and a of full-length DNA is observed in WRN and pol ε of tetraplex of DNA polymerase is not limited to the polymerase but to the helicase Our to coli RecQ can unwind G′2 and pol δ to synthesize the WRN is not RecQ and WRN to the of DNA helicases Martin G.M. PubMed Scopus Google these are with the that replicative of hairpin structures in coli can a RecQ PubMed Google to RecQ and WRN, coli UvrD that can unwind the tetraplex not pol δ at secondary on these that DNA helicases of the RecQ may to tetraplex secondary structures in DNA by pol in and that of the tetraplex by is not to of the tetraplex by DNA the suggest a a concerted action of DNA by WRN and DNA synthesis by The may be a of these a WRN and pol δ PubMed Scopus Google The of a effect of WRN on replication of tetraplex DNA template by pol that the of pol δ is to synthesis with that an in the WRN and pol δ Scopus Google be that the pol δ that to with WRN PubMed Scopus Google is not the that is of pol δ by WRN. these findings are not is that WRN with the of pol δ but the of PubMed Scopus Google effect on pol δ of the tetraplex by WRN DNA of the tetraplex is not to of the the d(CGG)n a hairpin hairpin structures effectively impede of synthesis by pol α and pol ε WRN can unwind the tetraplex synthesis by pol α and pol ε with of hairpin structures that the of these synthesis by pol δ, to of the hairpin tetraplex by WRN, in of the DNA secondary structures and of full-length DNA of WRN to tetraplex structures of d(CGG)n and to pausing by pol δ at these template be of d(CGG)n are not to the of the a of d(CGG)n in the in PubMed Scopus Google PubMed Scopus Google is that and by DNA may be the of WRN of of DNA replication of d(CGG)n may in the of and these structures be by WRN helicase, impede polymerase and the PubMed Scopus Google observed in WS WRN protein PubMed Scopus Google stalled forks the of the that in the of DNA that are of WS Martin G.M. PubMed Scopus Google that DNA d(CGG)n hairpin tetraplex structures impede DNA synthesis by three replicative DNA pol α, pol δ, and pol ε. The constraints imposed on DNA synthesis can be by the action of a DNA helicase that can tetraplex structures. that of polymerase with to the polymerase and the The of a RecQ helicase that can unwind d(CGG)n hairpin and tetraplex and pol δ synthesis of full-length products. Werner Syndrome (WS),1characterized by premature aging and genomic instability (1Epstein C.J. Martin G.M. Schultz A.L. Motulsky A.G. Medicine. 1966; 45: 177-221Crossref PubMed Scopus (735) Google is a of in the WS The encoded by the WS gene, WRN, a by DNA helicases of the RecQ Martin G.M. PubMed Scopus Google of DNA helicases is by Escherichia coli RecQ PubMed Scopus Google PubMed Google PubMed Scopus Google PubMed Scopus Google and PubMed Google PubMed Scopus Google and and PubMed Scopus Google RecQ DNA helicases in Google PubMed Scopus Google WRN is of the RecQ helicase in that an exonuclease PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google WRN protein to in to an 3′ → 5′ DNA helicase an intrinsic 3′ → 5′ DNA exonuclease PubMed Scopus Google PubMed Scopus Google WRN helicase of DNA a 3′ DNA a helicase DNA Martin G.M. PubMed Scopus Google PubMed Scopus Google WRN that the is of in The of WRN can be by the replication protein PubMed Scopus Google in WRN DNA PubMed Scopus Google WRN can unwind alternate DNA including DNA PubMed Scopus Google Holliday PubMed Scopus Google and triplex DNA PubMed Scopus Google of WRN and in The of WS PubMed Scopus Google PubMed Scopus Google to the PubMed Scopus Google and the of a and WRN and the replicative DNA pol δ PubMed Scopus Google Scopus Google the that WRN is in of DNA is the a function of WRN helicase may be to alternate DNA structures of the replication that impede the of DNA to the function of the helicase in PubMed Google DNA tetraplex structures in PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google of DNA are by that are by and by the of tetraplex DNA structures in is by DNA and the to on in PubMed Scopus Google and in PubMed Scopus Google PubMed Scopus Google in is the of hairpin PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and tetraplex structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google by the in to fragile X and tetraplex structures of to of DNA polymerases in DNA synthesis PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google of replicative DNA polymerases in polymerase and of the report that DNA synthesis by eukaryotic DNA polymerases is by hairpin and bimolecular G′2 tetraplex structures of a in template of WRN helicase, however, pol δ to traverse these template secondary structures and to synthesize full-length that the of WRN to polymerase at these secondary structures is and limited to pol δ. and and and by by WRN protein to by the by PubMed Scopus Google of WRN protein a of WRN on a RecQ helicase by of and UvrD helicase a DNA pol δ and pol to PubMed Scopus Google of pol δ and pol DNA polymerase and DNA polymerase ε the of and of of with by and to the the by the DNA with template by a with an of template DNA in The at and the to by to in to template DNA in an The with to a DNA of in the presence of in a of The at to of tetraplex the of to by the of of the DNA in of a in The at at a of to tetraplex of the and tetraplex DNA by and the The in and at of by the DNA with and in of the DNA at of the tetraplex DNA the of of to a of The hairpin template in DNA template by of DNA polymerases in the presence of of DNA DNA synthesis in that in a of and of and the of template not at the by on and of The and The and by by in that in of the tetraplex DNA with of coli coli UvrD at The by the of of a and and of tetraplex DNA by of a in at a of by PubMed Scopus Google and and and by by WRN protein to by the by PubMed Scopus Google of WRN protein a of WRN on a RecQ helicase by of and UvrD helicase a DNA pol δ and pol to PubMed Scopus Google of pol δ and pol DNA polymerase and DNA polymerase ε the of and of and and by by WRN protein to by the by PubMed Scopus Google of WRN protein a of WRN on a RecQ helicase by of and UvrD helicase a DNA pol δ and pol to PubMed Scopus Google of pol δ and pol DNA polymerase and DNA polymerase ε the of and of of with by and to the the by the DNA with template by a with an of template DNA in The at and the to by to in to template DNA in an The with to a DNA of in the presence of in a of The at to of tetraplex the of to by the of of the DNA in of a in The at at a of to tetraplex of the and tetraplex DNA by and the The in and at of by the DNA with and in of the DNA at of the tetraplex DNA the of with by and to the the by the DNA with template by a The with an of template DNA in The at and the to by to in to template DNA in an The with to a DNA of in the presence of in a of The at to of tetraplex the of to by the of of the DNA in of a in The at at a of to tetraplex of the and tetraplex DNA by and the The in and at of by the DNA with and in of the DNA at of the tetraplex DNA the of of to a of The hairpin template in to a of The hairpin template in DNA template by of DNA polymerases in the presence of of DNA DNA synthesis in that in a of and of and the of template not at the by on and of The and The and by by in that in of the tetraplex DNA with of coli coli UvrD at The by the of of a and and of tetraplex DNA by of a in at a of by PubMed Scopus Google DNA DNA template by of DNA polymerases in the presence of of DNA DNA synthesis in that in a of and of and the of template not at the by on and of The and The and by by in that in of the tetraplex DNA with of coli coli UvrD at The by the of of a and and of tetraplex DNA by of a in at a of by PubMed Scopus Google DNA DNA template by of DNA polymerases in the presence of of DNA DNA synthesis in that in a of and of and the of template not at the by on and of The and The and by by DNA template by of DNA polymerases in the presence of of DNA DNA synthesis in that in a of and of and the of template not at the by on and of The and The and by by DNA in that in of the tetraplex DNA with of coli coli UvrD at The by the of of a and and of tetraplex DNA by of a in at a of by PubMed Scopus Google in that in of the tetraplex DNA with of coli coli UvrD at The by the of of a and and of tetraplex DNA by of a in at a of by PubMed Scopus Google DNA that WRN in are not of to in DNA WS including a of DNA and a of PubMed Scopus Google PubMed Scopus Google these are to the PubMed Scopus Google The and of WRN with a replicative DNA pol δ PubMed Scopus Google Scopus Google a role of WRN in the that of pol δ by WRN in the of the pol δ Scopus Google that WRN may not in DNA with the that WRN can unwind alternate DNA structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google to that WRN may be in replication at forks by DNA stalled by DNA secondary structures. report in by the effect of WRN on the of synthesis by pol δ hairpin and tetraplex DNA bimolecular tetraplex hairpin of the d(CGG)n template secondary structures. in the of PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google The of d(CGG)n to PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and to structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google in the of that to fragile X and tetraplex structures of d(CGG)n to the of DNA polymerases in PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and in G.M. PubMed Scopus Google a DNA template that a hairpin a bimolecular G′2 tetraplex in the presence of with that the template G′2 hairpin and tetraplex structures a to DNA synthesis by three eukaryotic replicative DNA α, δ, and ε and of a by three DNA polymerases the of the with DNA the of polymerase is that of the is the DNA the of the tetraplex not of WRN pausing by pol δ at the tetraplex a of the full-length DNA of that of pol δ pausing is a of the tetraplex d(CGG)n of WRN. WRN is to unwind the template G′2 tetraplex in the presence of in not is with that can in PubMed Scopus Google the helicase WRN protein that is to unwind DNA PubMed Scopus Google Martin G.M. PubMed Scopus Google to of pol δ by the of of WRN and pol δ, that of polymerase pausing that of the tetraplex synthesis with DNA synthesis by pol δ to synthesis the G′2 tetraplex replicative and to full-length DNA in the presence of WRN by to be limited to pol δ. WRN not pol α the pol δ pol to traverse the template tetraplex and and a of full-length DNA is observed in WRN and pol ε of tetraplex of DNA polymerase is not limited to the polymerase but to the helicase Our to coli RecQ can unwind G′2 and pol δ to synthesize the WRN is not RecQ and WRN to the of DNA helicases Martin G.M. PubMed Scopus Google these are with the that replicative of hairpin structures in coli can a RecQ PubMed Google to RecQ and WRN, coli UvrD that can unwind the tetraplex not pol δ at secondary on these that DNA helicases of the RecQ may to tetraplex secondary structures in DNA by pol in and that of the tetraplex by is not to of the tetraplex by DNA the suggest a a concerted action of DNA by WRN and DNA synthesis by The may be a of these a WRN and pol δ PubMed Scopus Google The of a effect of WRN on replication of tetraplex DNA template by pol that the of pol δ is to synthesis with that an in the WRN and pol δ Scopus Google be that the pol δ that to with WRN PubMed Scopus Google is not the that is of pol δ by WRN. these findings are not is that WRN with the of pol δ but the of PubMed Scopus Google effect on pol δ of the tetraplex by WRN DNA of the tetraplex is not to of the the d(CGG)n a hairpin hairpin structures effectively impede of synthesis by pol α and pol ε WRN can unwind the tetraplex synthesis by pol α and pol ε with of hairpin structures that the of these synthesis by pol δ, to of the hairpin tetraplex by WRN, in of the DNA secondary structures and of full-length DNA of WRN to tetraplex structures of d(CGG)n and to pausing by pol δ at these template be of d(CGG)n are not to the of the a of d(CGG)n in the in PubMed Scopus Google PubMed Scopus Google is that and by DNA may be the of WRN of of DNA replication of d(CGG)n may in the of and these structures be by WRN helicase, impede polymerase and the PubMed Scopus Google observed in WS WRN protein PubMed Scopus Google stalled forks the of the that in the of DNA that are of WS Martin G.M. PubMed Scopus Google that DNA d(CGG)n hairpin tetraplex structures impede DNA synthesis by three replicative DNA pol α, pol δ, and pol ε. The constraints imposed on DNA synthesis can be by the action of a DNA helicase that can tetraplex structures. that of polymerase with to the polymerase and the The of a RecQ helicase that can unwind d(CGG)n hairpin and tetraplex and pol δ synthesis of full-length products. The DNA that WRN in are not of to in DNA WS including a of DNA and a of PubMed Scopus Google PubMed Scopus Google these are to the PubMed Scopus Google The and of WRN with a replicative DNA pol δ PubMed Scopus Google Scopus Google a role of WRN in the that of pol δ by WRN in the of the pol δ Scopus Google that WRN may not in DNA with the that WRN can unwind alternate DNA structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google to that WRN may be in replication at forks by DNA stalled by DNA secondary structures. report in by the effect of WRN on the of synthesis by pol δ hairpin and tetraplex DNA structures. We bimolecular tetraplex hairpin of the d(CGG)n template secondary structures. in the of PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google The of d(CGG)n to PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and to structures PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google in the of that to fragile X and tetraplex structures of d(CGG)n to the of DNA polymerases in PubMed Scopus Google PubMed Scopus Google PubMed Scopus Google and in G.M. PubMed Scopus Google We a DNA template that a hairpin a bimolecular G′2 tetraplex in the presence of with that the template G′2 hairpin and tetraplex structures a to DNA synthesis by three eukaryotic replicative DNA α, δ, and ε and of a by three DNA polymerases the of the with DNA the of polymerase is that of the is the DNA the of the tetraplex not of WRN pausing by pol δ at the tetraplex a of the full-length DNA of that of pol δ pausing is a of the tetraplex d(CGG)n of WRN. WRN is to unwind the template G′2 tetraplex in the presence of in not is with that can in PubMed Scopus Google the helicase WRN protein that is to unwind DNA PubMed Scopus Google Martin G.M. PubMed Scopus Google to of pol δ by the of of WRN and pol δ, that of polymerase pausing that of the tetraplex synthesis with DNA synthesis by pol δ The to synthesis the G′2 tetraplex replicative and to full-length DNA in the presence of WRN by to be limited to pol δ. WRN not pol α the pol δ pol to traverse the template tetraplex and and a of full-length DNA is observed in WRN and pol ε The of tetraplex of DNA polymerase is not limited to the polymerase but to the helicase Our to coli RecQ can unwind G′2 and pol δ to synthesize the WRN is not RecQ and WRN to the of DNA helicases Martin G.M. PubMed Scopus Google these are with the that replicative of hairpin structures in coli can a RecQ PubMed Google to RecQ and WRN, coli UvrD that can unwind the tetraplex not pol δ at secondary on these that DNA helicases of the RecQ may to tetraplex secondary structures in DNA by pol δ. in and that of the tetraplex by is not to of the tetraplex by DNA the suggest a a concerted action of DNA by WRN and DNA synthesis by The may be a of these a WRN and pol δ PubMed Scopus Google The of a effect of WRN on replication of tetraplex DNA template by pol that the of pol δ is to synthesis with that an in the WRN and pol δ Scopus Google be that the pol δ that to with WRN PubMed Scopus Google is not the that is of pol δ by WRN. these findings are not is that WRN with the of pol δ but the of PubMed Scopus Google effect on pol δ of the tetraplex by WRN DNA of the tetraplex is not to of the the d(CGG)n a hairpin hairpin structures effectively impede of synthesis by pol α and pol ε WRN can unwind the tetraplex synthesis by pol α and pol ε with of hairpin structures that the of these synthesis by pol δ, to of the hairpin tetraplex by WRN, in of the DNA secondary structures and of full-length DNA The of WRN to tetraplex structures of d(CGG)n and to pausing by pol δ at these template be of d(CGG)n are not to the of the a of d(CGG)n in the in PubMed Scopus Google PubMed Scopus Google is that and by DNA may be the of WRN of of DNA replication of d(CGG)n may in the of and these structures be by WRN helicase, impede polymerase and the PubMed Scopus Google observed in WS WRN protein PubMed Scopus Google stalled forks the of the that in the of DNA that are of WS Martin G.M. PubMed Scopus Google that DNA d(CGG)n hairpin tetraplex structures impede DNA synthesis by three replicative DNA pol α, pol δ, and pol ε. The constraints imposed on DNA synthesis can be by the action of a DNA helicase that can tetraplex structures. that of polymerase with to the polymerase and the The of a RecQ helicase that can unwind d(CGG)n hairpin and tetraplex and pol δ synthesis of full-length products.