Characterization of the DNA-unwinding Activity of Human RECQ1, a Helicase Specifically Stimulated by Human Replication Protein A

The RecQ helicases are involved in several aspects of DNA metabolism. Five members of the RecQ family have been found in humans, but only two of them have been carefully characterized, BLM and WRN. In this work, we describe the enzymatic characterization of RECQ1. The helicase has 3′ to 5′ polarity, cannot start the unwinding from a blunt-ended terminus, and needs a 3′-single-stranded DNA tail longer than 10 nucleotides to open the substrate. However, it was also able to unwind a blunt-ended duplex DNA with a “bubble” of 25 nucleotides in the middle, as previously observed for WRN and BLM. We show that only short DNA duplexes (100 bp). Our studies done with Escherichia colisingle-strand binding protein (SSB) indicate that the helicase activity of RECQ1 is specifically stimulated by hRPA. This finding suggests that RECQ1 and hRPA may interact also in vivo and function together in DNA metabolism. Comparison of the present results with previous studies on WRN and BLM provides novel insight into the role of the N- and C-terminal domains of these helicases in determining their substrate specificity and in their interaction with hRPA. The RecQ helicases are involved in several aspects of DNA metabolism. Five members of the RecQ family have been found in humans, but only two of them have been carefully characterized, BLM and WRN. In this work, we describe the enzymatic characterization of RECQ1. The helicase has 3′ to 5′ polarity, cannot start the unwinding from a blunt-ended terminus, and needs a 3′-single-stranded DNA tail longer than 10 nucleotides to open the substrate. However, it was also able to unwind a blunt-ended duplex DNA with a “bubble” of 25 nucleotides in the middle, as previously observed for WRN and BLM. We show that only short DNA duplexes (100 bp). Our studies done with Escherichia colisingle-strand binding protein (SSB) indicate that the helicase activity of RECQ1 is specifically stimulated by hRPA. This finding suggests that RECQ1 and hRPA may interact also in vivo and function together in DNA metabolism. Comparison of the present results with previous studies on WRN and BLM provides novel insight into the role of the N- and C-terminal domains of these helicases in determining their substrate specificity and in their interaction with hRPA. human replication protein A single-stranded DNA nucleotides bovine serum albumin E. coli single-strand binding protein DNA and RNA helicases are a ubiquitous class of enzymes characterized by their capacity to unwind and translocate along DNA or RNA in reactions that are coupled to the binding and hydrolysis of a 5′-NTP (1Lohman T.M. Bjornson K.P. Annu. Rev. Biochem. 1996; 65: 169-214Crossref PubMed Scopus (665) Google Scholar). These enzymes are involved in most aspects of nucleic acid metabolism, such as DNA replication, DNA repair, recombination, transcription, RNA processing, and translation (2Matson S.W. Bean D.W. George J.W. Bioessays. 1994; 16: 13-22Crossref PubMed Scopus (266) Google Scholar). Alterations of genes that code for helicases cause several human disorders (3Ellis N.A. Curr. Opin. Genet. Dev. 1997; 7: 354-363Crossref PubMed Scopus (115) Google Scholar). For example, two genes, XPB and XPD, encode for helicases that are defective in individuals with xeroderma pigmentosum and Cockayne's syndrome, respectively (4Weeda G. van Ham R.C. Vermeulen W. Bootsma D. van der Eb A.J. Hoeijmakers J.H. Cell. 1990; 62: 777-791Abstract Full Text PDF PubMed Scopus (384) Google Scholar). Bloom's, Werner's, and Rothmund-Thomson syndromes are additional genetic disorders that arise as a consequence of abnormalities in three different members of the RecQ family of helicases named BLM, WRN, and RECQ4, respectively (5Ellis N.A. Groden J., Ye, T.Z. Straughen J. Lennon D.J. Ciocci S. Proytcheva M. German J. Cell. 1995; 83: 655-666Abstract Full Text PDF PubMed Scopus (1200) Google Scholar, 6Yu C.E. Oshima J., Fu, Y.H. Wijsman E.M. Hisama F. Alisch R. Matthews S. Nakura J. Miki T. Ouais S. Martin G.M. Mulligan J. Schellenberg G.D. Science. 1996; 272: 258-262Crossref PubMed Scopus (1473) Google Scholar, 7Kitao S. Lindor N.M. Shiratori M. Furuichi Y. Shimamoto A. Genomics. 1999; 61: 268-276Crossref PubMed Scopus (143) Google Scholar). In all three syndromes, cells from affected individuals show inherent genomic instability, indicating that these RecQ helicases play a role in the maintenance of chromosome stability. The name RecQ derives from the first helicase of the family discovered in Escherichia coli (8Umezu K. Nakayama H. J. Mol. Biol. 1993; 230: 1145-1150Crossref PubMed Scopus (81) Google Scholar, 9Nakayama K. Irino N. Nakayama H. Mol. Gen. Genet. 1985; 200: 266-271Crossref PubMed Scopus (123) Google Scholar). Successively, members of the RecQ helicase family have been found in organisms that range from bacteria to plants and animals (10Kusano K. Berres M.E. Engels W.R. Genetics. 1999; 151: 1027-1039PubMed Google Scholar, 11Ozsoy A.Z. Sekelsky J.J. Matson S.W. Nucleic Acids Res. 2001; 29: 2986-2993Crossref PubMed Scopus (20) Google Scholar). In microorganisms likeE. coli, Saccharomyces cerevisiae, andSchizosaccharomyces pombe, only one representative per species is present, whereas higher eukaryotes contain more than one RecQ helicase. For example, five members of the RecQ family have been found so far in human cells, RECQ1, WRN, BLM, RECQ4, and RECQ5 (12Karow J.K., Wu, L. Hickson I.D. Curr. Opin. Genet. Dev. 2000; 10: 32-38Crossref PubMed Scopus (160) Google Scholar). All of them share a common central domain of ∼450 amino acids containing seven highly conserved motifs also present in several helicases from other families (13Gorbalenya A.E. Koonin E.V. Donchenko A.P. Blinov V.M. Nucleic Acids Res. 1989; 17: 4713-4730Crossref PubMed Scopus (821) Google Scholar). Among these motifs are an ATP-binding sequence (Walker A box) and the DEXH box, which is instead characteristic of the RecQ family. The RecQ helicases are divided in two classes according to the length of the N- and C-terminal domains. E. coli RecQ, human RECQ1, and RECQ5 form the first group of RecQ helicases. They are characterized by short N- and C-terminal domains, and their sequences are between 400 and 650 amino acids long. The WRN, BLM, RECQ4, Sgs1p (from budding yeast), and Rqh1p (from fission yeast) helicases are part of the second group because they have extended N- and C-terminal tails and are all between 1300 and 1500 amino acids long. The function of these extended tails is still under investigation. One possibility is that the additional portions mediate the interaction of these helicases with other proteins. In fact, several proteins have been shown to interact with these longer helicases, such as replication protein A (14Brosh R.M., Jr. Orren D.K. Nehlin J.O. Ravn P.H. Kenny M.K. Machwe A. Bohr V.A. J. Biol. Chem. 1999; 274: 18341-18350Abstract Full Text Full Text PDF PubMed Scopus (255) Google Scholar, 15Brosh R.M., Jr., Li, J.L. Kenny M.K. Karow J.K. Cooper M.P. Kureekattil R.P. Hickson I.D. Bohr V.A. J. Biol. Chem. 2000; 275: 23500-23508Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar), proliferating cell nuclear antigen (16Lebel M. Spillare E.A. Harris C.C. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar), DNA (16Lebel M. Spillare E.A. Harris C.C. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar), L. J. Biol. Chem. 2000; 275: Full Text Full Text PDF Google Scholar, M.P. Machwe A. Orren D.K. D. Bohr V.A. Dev. 2000; Google Scholar, Bohr V.A. Nucleic Acids Res. PubMed Scopus Google Scholar), DNA E. S. A. 2000; PubMed Scopus Google Scholar), and E.A. C.E. Schellenberg G.D. Harris C.C. Dev. 1999; PubMed Scopus Google Scholar, R. Spillare E.A. D. Li, J.L. Hickson I.D. E. R.M., Jr. Bohr V.A. Harris C.C. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). A common of all RecQ helicases so far is that they unwind DNA with a 3′ to 5′ the other only the activity and substrate specificity of the human BLM and WRN helicases have been R. Spillare E.A. D. Li, J.L. Hickson I.D. E. R.M., Jr. Bohr V.A. Harris C.C. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, L. R.M., Jr. Hickson I.D. Bohr V.A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, R.M., Jr. J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. D.W. S. J. D.J. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Google Scholar, Oshima J. Nucleic Acids Res. PubMed Scopus Google Scholar), whereas or is so far on the of the other three human helicases, RECQ1, RECQ4, and RECQ5 J.J. G.M. Nucleic Acids Res. 1999; PubMed Scopus Google Scholar, S. Shimamoto A. M. Lindor N.M. Furuichi Y. Genet. 1999; PubMed Scopus Google Scholar). In this work, we describe the enzymatic characterization of the helicase activity of human RECQ1. The protein was from cells a to the one in for the of several other human DNA helicases A. A. G. A. Nucleic Acids Res. 2001; 29: PubMed Scopus Google Scholar, M. A. A. A. Nucleic Acids Res. 1999; PubMed Scopus Google Scholar, N. R. K. A. Nucleic Acids Res. 1990; PubMed Scopus Google Scholar, N. K. R. A. D. A. Nucleic Acids Res. PubMed Scopus Google Scholar). The possibility that the helicase activity of RECQ1 may be specifically stimulated by human replication protein A as in the of the and helicases, was also Comparison of results with the previously hRPA of the WRN and BLM helicases provides novel insight into the that the N- and C-terminal tails and the central acid domain of these RecQ helicases play in the interaction with hRPA. All bovine serum and from The single-stranded DNA the serum to the cells, and from All for the different from of the an studies with a All to the DNA from The from The and for protein from hRPA containing all three and was in and from E. coli according to the previously J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). cells in with and and as previously N. R. K. A. Nucleic Acids Res. 1990; PubMed Scopus Google Scholar). All the of RECQ1 and as A and and The of or in all was to for the proteins from the different The RECQ1 helicase was from of The cell and with the by Nucleic Acids Res. PubMed Scopus Google Scholar). Successively, an additional with was done to specifically for proteins that to The proteins by by in a in and to a with A N. K. R. A. Nucleic Acids Res. 1993; PubMed Scopus Google Scholar). in A All and the unwinding activity of was with a DNA substrate as A. A. G. A. Nucleic Acids Res. 2001; 29: PubMed Scopus Google Scholar). was first in and a with The proteins to the a of in All the of the and a was with the for the and the helicase between and was in and a for the of was with a of of in A The together and with The DNA in the helicase are in They of different to or to of different to a The sequence of the for the of the of unwinding and is the as that previously N. K. R. A. Nucleic Acids Res. PubMed Scopus Google Scholar), as are the sequences of three to the A. A. G. A. Nucleic Acids Res. 2001; 29: PubMed Scopus Google Scholar, N. K. R. A. Nucleic Acids Res. PubMed Scopus Google Scholar). The substrate in was to nucleotides of The blunt-ended duplex was by to The substrate in was by to a to the for the 25 in the with tails of different a to with of and nucleotides The substrate with a of was by of a of the The for the was to of whereas the was to as 10 and of in a as for for for and for and for For all 25 of the with and of to in 10 and The was for and to substrate was by a The substrate was as The containing the was by and in with RNA from the a RNA M. A. A. A. Nucleic Acids Res. 1999; PubMed Scopus Google Scholar). A RNA to the of was and the with and of of with of for and to by The by a The helicase the unwinding of a DNA from a duplex DNA The 10 bovine serum albumin and helicase substrate The helicase to be was to the and for and the was by the addition of 10 and The of the by on a The was and the of DNA unwinding was by One of DNA helicase is as the of enzyme unwinding of the substrate in in in the range of enzyme The was by and the previously A. A. G. A. Nucleic Acids Res. 2001; 29: PubMed Scopus Google N. R. A. A. S. K. L. J. J. S. S. A. J. 1994; PubMed Scopus Google Scholar, PubMed Scopus Google Scholar). for the of RECQ1 on a in and for The protein also under the The and of from the of the an and for helicase For a was in the with The of RECQ1 was first from to and the The was a of of and for helicase The was under the The of and The is to is the of the is the is the of the The of RECQ1 was from the of the of the proteins. The of RECQ1 was from the and the the previously PubMed Scopus Google Scholar). The and containing RECQ1 and with bovine The by and by The human helicase RECQ1 was from the nuclear of cells the under The was on a for of The only a of Successively, the was from the with and by for protein to the human DNA helicase RECQ1 found in the The five helicases of the RecQ family that have been found in human cells are characterized by a conserved central domain of ∼450 amino the other the 10 found by have sequences that are for RECQ1, to be the of the to sequences in the central domain of the two in the and two in the C-terminal tail acid sequences of the present in RECQ1 by in a helicase family. is a of members of the RecQ family of helicases from E. coli to The conserved central domain in helicase is shown as a indicate the of the of RECQ1 found by we the of RECQ1 by and a previously PubMed Scopus Google Scholar, N. A. R. D. A. Nucleic Acids Res. 1995; PubMed Scopus Google Scholar). The that RECQ1 has a of and a of to a of that the protein as a in the other studies to be done under different and with additional to more on the of this studies under a of unwinding in with The the of the is of that more than one of RECQ1 be involved in DNA as in the of other helicases (1Lohman T.M. Bjornson K.P. Annu. Rev. Biochem. 1996; 65: 169-214Crossref PubMed Scopus (665) Google Scholar). in the of enzyme that the unwinding was for to 10 and from with longer The helicase that and are for DNA In studies that the for DNA unwinding is between and we also observed that the addition of the unwinding activity of RECQ1. This be by previous studies that the of increases the of proteins for DNA D. S. S. G. A. A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Nucleic Acids Res. 1990; PubMed Scopus Google and of RECQ1 of RECQ1 in the for The of enzyme is in the whereas the substrate was in all the of unwinding RECQ1 and the for the The are in the The and are enzyme and The only that was on the helicase activity of human RECQ1 is that it DNA with 3′ to 5′ polarity, the other members of the RecQ family characterized so far M. J. T. M. T. J. Biochem. 1994; PubMed Scopus Google Scholar). This of unwinding was by that RECQ1 needs a tail to unwind the substrate this a of with different and with of the to novel on the substrate specificity of RECQ1 with a to unwound by RECQ1, of the or of tails the the or However, the duplex was to the substrate be unwound to has been observed for the BLM and WRN helicases Karow J.K. R.M., Jr. Bohr V.A. Hickson I.D. Nucleic Acids Res. 2001; 29: PubMed Scopus Google Scholar), RECQ1 was able to unwind a substrate with a of 25 in the helicases previously in have been shown to be able to unwind as as duplexes A. A. G. A. Nucleic Acids Res. 2001; 29: PubMed Scopus Google in RECQ1 unwind RNA indicating that it can only as a DNA helicase. a of with tails of and to the of tail length on the unwinding activity of RECQ1 studies done with this of that only the with tails longer than 10 be unwound by RECQ1 hRPA specifically the activity of the WRN and BLM helicases (14Brosh R.M., Jr. Orren D.K. Nehlin J.O. Ravn P.H. Kenny M.K. Machwe A. Bohr V.A. J. Biol. Chem. 1999; 274: 18341-18350Abstract Full Text Full Text PDF PubMed Scopus (255) Google Scholar, 15Brosh R.M., Jr., Li, J.L. Kenny M.K. Karow J.K. Cooper M.P. Kureekattil R.P. Hickson I.D. Bohr V.A. J. Biol. Chem. 2000; 275: 23500-23508Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar). In we that also the helicase activity of RECQ1 was specifically stimulated by the addition of hRPA. The RECQ1 helicase unwind a DNA substrate with a duplex of but with the addition of hRPA or E. coli single-strand binding protein the substrate was and studies in the of the unwinding was in A and the other a of higher than that of hRPA only of the substrate was unwound more insight into the of by these single-strand binding was as a function of the of the of single-strand binding protein to the of by the of the substrate in nucleotides divided by the of by In this the into that hRPA binding to DNA Annu. Rev. Biochem. 1997; PubMed Scopus Google Scholar), whereas T.M. M.E. Annu. Rev. Biochem. 1994; PubMed Scopus Google The a of hRPA that the in the helicase of the was whereas unwinding was a of of of the duplex was in the of but unwinding was observed with RECQ1 helicase This was by the results with the duplex This substrate be unwound only hRPA was present, whereas to the unwinding a higher than that for hRPA and of of unwinding of a duplex substrate in the of hRPA. The of unwinding RECQ1 and in the of hRPA or The of RECQ1 was The are in the The role of the five members of the RecQ family of helicases found in is still and under (12Karow J.K., Wu, L. Hickson I.D. Curr. Opin. Genet. Dev. 2000; 10: 32-38Crossref PubMed Scopus (160) Google Scholar, L. Hickson I.D. Science. 2001; PubMed Scopus Google Scholar). indicate that the human RecQ helicases play a role in the maintenance of chromosome and to their in different aspects of DNA metabolism, such as DNA replication, repair, and (12Karow J.K., Wu, L. Hickson I.D. Curr. Opin. Genet. Dev. 2000; 10: 32-38Crossref PubMed Scopus (160) Google Scholar, L. Hickson I.D. Science. 2001; PubMed Scopus Google Scholar). In of the only RecQ family in S. to a of DNA metabolism, but cause cell K. L. Science. 1997; PubMed Scopus Google Scholar). This also to the human cell I.D. J.L. L. Biochem. 2001; 29: PubMed Google in this it is that other members of the family for on the substrate specificity of RecQ helicases and on their of DNA unwinding is for a of their the other only the enzymatic activity of two human RecQ helicases, WRN and BLM, has been carefully to I.D. J.L. L. Biochem. 2001; 29: PubMed Google Scholar). We the human RECQ1 helicase from nuclear and it by this is one of the first helicases of the RecQ family discovered in human cells, and on and was J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, M. H. S. J. T. S. K. T. M. K. H. F. T. Nucleic Acids Res. 1994; PubMed Scopus (143) Google Scholar). The only on the of the RecQ helicases from studies on the BLM it was by and that it in J.K. Hickson I.D. Curr. Biol. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). the other that RECQ1 to form than suggests that the five helicases of the RecQ family may different and may to unwind In the of the as a function of RECQ1 is of that more than one of RECQ1 be involved in DNA as in the of other helicases (1Lohman T.M. Bjornson K.P. Annu. Rev. Biochem. 1996; 65: 169-214Crossref PubMed Scopus (665) Google the possibility that a on the substrate cannot be The 3′ to 5′ of unwinding was the only on the helicase activity of RECQ1 M. J. T. M. T. J. Biochem. 1994; PubMed Scopus Google and has been also by The substrate specificity of RECQ1 was with a of DNA of different and was previously observed for the BLM and WRN helicases Karow J.K. R.M., Jr. Bohr V.A. Hickson I.D. Nucleic Acids Res. 2001; 29: PubMed Scopus Google Scholar), RECQ1 cannot unwind blunt-ended DNA In the E. helicase is able to duplex unwinding from a blunt-ended Dev. PubMed Scopus Google Scholar). RECQ1 is able to unwind of blunt-ended duplexes because it unwind a blunt-ended DNA substrate with a in the in with been previously observed for WRN and BLM Karow J.K. R.M., Jr. Bohr V.A. Hickson I.D. Nucleic Acids Res. 2001; 29: PubMed Scopus Google Scholar). on the short of N- and C-terminal domains, RECQ1 is the human RecQ the three WRN, and that most the E. For this it have been that RECQ1 have to E. coli RecQ than the other two human helicases. the other that the for the substrate specificity of these enzymes in the conserved central domain than in the N- and C-terminal domains and indicate that RecQ helicases from different organisms have different substrate We also the of the length of the tails on the unwinding activity of RECQ1 length studies have been on other human RecQ helicases, but it was shown that Sgs1p from S. is able to unwind with of only Our results indicate that RECQ1 from Sgs1p because a DNA with a of 10 was unwound and only the tail length was to 25 of the substrate was unwound A is that RECQ1 needs a tail longer than 10 to the substrate and to start the A common of the human RecQ helicases is that they are able to unwind DNA but have shown that the addition of hRPA the processivity of WRN and BLM (14Brosh R.M., Jr. Orren D.K. Nehlin J.O. Ravn P.H. Kenny M.K. Machwe A. Bohr V.A. J. Biol. Chem. 1999; 274: 18341-18350Abstract Full Text Full Text PDF PubMed Scopus (255) Google Scholar, 15Brosh R.M., Jr., Li, J.L. Kenny M.K. Karow J.K. Cooper M.P. Kureekattil R.P. Hickson I.D. Bohr V.A. J. Biol. Chem. 2000; 275: 23500-23508Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar). In with these we observed that RECQ1 was to unwind a duplex DNA under but the substrate be unwound hRPA was to the addition of the substrate also be more than only of the duplex was The of hRPA in the helicase activity of RECQ1 suggests that hRPA an additional role in the unwinding than the the of the This is by the results with the duplex substrate. done in the of hRPA or that hRPA was for the unwinding of the duplex whereas was to the unwinding of this substrate. These indicate that hRPA and RECQ1, are for the unwinding of and that these two proteins may interact in A interaction between RECQ1 and hRPA indicate a role of this helicase in replication, recombination, or repair, all in which hRPA has been shown to be involved Annu. Rev. Biochem. 1997; PubMed Scopus Google Scholar). Our also novel on the of the N- and central domains of the RecQ helicases in the interaction with hRPA. studies have shown that the of WRN a 3′ 5′ domain and the interaction of WRN with the L. J. Biol. Chem. 2000; 275: Full Text Full Text PDF Google Scholar, Bohr V.A. Nucleic Acids Res. PubMed Scopus Google and proliferating cell nuclear antigen (16Lebel M. Spillare E.A. Harris C.C. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar), whereas the is for the interaction with E.A. C.E. Schellenberg G.D. Harris C.C. Dev. 1999; PubMed Scopus Google Scholar, G. J. C.E. Schellenberg G.D. M. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google and the Bohr V.A. Nucleic Acids Res. PubMed Scopus Google Scholar). The extended N- and C-terminal domains of the BLM helicase mediate interaction with L. H. H. Hickson I.D. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google and L. Hickson I.D. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). the other on the of the N- and C-terminal domains of these helicases in the interaction with hRPA is The that WRN and BLM interact with hRPA to the that the extended N- and C-terminal domains of these two helicases may also be involved in this binding However, that the central domain of these RecQ helicases be the one involved in the interaction of RECQ1, WRN, and BLM with hRPA because RECQ1 the extended N- and C-terminal domains of WRN and BLM. The that from studies is that the substrate specificity and activity of RECQ1 in to of the BLM and WRN helicases, different from of E. coli RecQ and budding the that RECQ1 with hRPA is in with previous studies done with BLM and WRN. These to that the extended N- and C-terminal domains of BLM and WRN are for the substrate specificity of these helicases and are involved in the interaction of these proteins with hRPA. The that all three helicases interact with hRPA suggests that they be involved in the and in a so the of one of them be for by the of the This is also by other studies that WRN and BLM interact L. R.M., Jr. Hickson I.D. Bohr V.A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and are involved in DNA in a K. S. Furuichi Y. T. PubMed Scopus Google Scholar). the other the that WRN and BLM, with their extended N- and C-terminal domains, can also interact with other such as and that they can also be involved in RECQ1 is However, more studies to be done to a of the of this family of human helicases. We are to for hRPA and the for the of hRPA The of and in the of cells is We for in the