Thermotoga maritima-Escherichia coli Chimeric Topoisomerases

Abstract

Bacterial topoisomerases I are generally composed of two domains as follows: a core domain, which contains all the conserved motifs involved in the trans-esterification reactions, and a carboxyl-terminal domain, highly variable in size and sequence. In the present work, we have addressed the question of the respective roles of the two domains in the different steps of the topoisomerization cycle. For this purpose, we prepared various recombinant topoisomerases from two model enzymes: topoisomerase I from the hyperthermophilic bacterium Thermotoga maritima and topoisomerase I from Escherichia coli. We compared the properties of the two core domains to that of the topoisomerases formed by combining the core domain of one enzyme to the carboxyl-terminal domain of the other. We found that, contrary to E. coli (Lima, C. D., Wang, J. C., and Mondragon, A. (1993) J. Mol. Biol. 232, 1213–1216), the core domain from T. maritima (TmTop65) is able to sustain by itself a complete topoisomerization cycle, although with low efficiency. Fusion of TmTop65 to the entire carboxyl-terminal domain from E. coli considerably increases binding efficiency, thermal stability, and DNA relaxation activity. Moreover, the chimera predominantly acquires the cleavage specificity of E. coli full-length topoisomerase. For the chimera obtained by fusion of the T. maritima carboxyl-terminal domain to the core EcTop67, very low DNA relaxation activity and binding are recovered, but formation of a covalent DNA adduct is impaired. Taken together, our results show that the presence and the nature of the carboxyl-terminal domain of bacterial topoisomerases I strongly determine their DNA binding efficiency and cleavage specificity but is not strictly required for strand passage. Bacterial topoisomerases I are generally composed of two domains as follows: a core domain, which contains all the conserved motifs involved in the trans-esterification reactions, and a carboxyl-terminal domain, highly variable in size and sequence. In the present work, we have addressed the question of the respective roles of the two domains in the different steps of the topoisomerization cycle. For this purpose, we prepared various recombinant topoisomerases from two model enzymes: topoisomerase I from the hyperthermophilic bacterium Thermotoga maritima and topoisomerase I from Escherichia coli. We compared the properties of the two core domains to that of the topoisomerases formed by combining the core domain of one enzyme to the carboxyl-terminal domain of the other. We found that, contrary to E. coli (Lima, C. D., Wang, J. C., and Mondragon, A. (1993) J. Mol. Biol. 232, 1213–1216), the core domain from T. maritima (TmTop65) is able to sustain by itself a complete topoisomerization cycle, although with low efficiency. Fusion of TmTop65 to the entire carboxyl-terminal domain from E. coli considerably increases binding efficiency, thermal stability, and DNA relaxation activity. Moreover, the chimera predominantly acquires the cleavage specificity of E. coli full-length topoisomerase. For the chimera obtained by fusion of the T. maritima carboxyl-terminal domain to the core EcTop67, very low DNA relaxation activity and binding are recovered, but formation of a covalent DNA adduct is impaired. Taken together, our results show that the presence and the nature of the carboxyl-terminal domain of bacterial topoisomerases I strongly determine their DNA binding efficiency and cleavage specificity but is not strictly required for strand passage. The control of DNA topology is critical for all essential processes that require opening of the double helix such as DNA replication, transcription, DNA repair, or recombination. In hyperthermophilic organisms, this control appears more critical, as high temperature also helps open the double-stranded DNA. Thus, topoisomerases as they are able to modify DNA structure (for reviews, see Refs. 2Champoux J.J. Annu. Rev. Biochem. 2001; 70: 369-413Crossref PubMed Scopus (2163) Google Scholar and 3Wang J.C. Nat. Rev. Mol. Cell. Biol. 2002; 3: 430-440Crossref PubMed Scopus (1877) Google Scholar) appear essential in these processes of adaptation to extreme temperatures. We have recently described the properties of the topoisomerase I from the hyperthermophilic bacterium, Thermotoga maritima, whose growth temperature is about 80 °C (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar). At 75 °C, this enzyme has an extremely high rate of relaxation activity on negatively supercoiled DNA. It belongs to the large family of topoisomerases IA present in all three domains of life, Bacteria, Archaea, and Eukarya (5Serre M.C. Duguet M. Prog. Nucleic Acid Res. Mol. Biol. 2003; 74: 37-81Crossref PubMed Scopus (13) Google Scholar, 6Tse-Dinh Y.-C. Biochim. Biophys. Acta. 1998; 1400: 19-27Crossref PubMed Scopus (51) Google Scholar). This type of enzymes catalyzes the transient breakage of one strand in double-stranded DNA to allow passage of the other DNA strand, or duplex, through the break and then religation of the broken strand. The different steps of the topoisomerization cycle occur through trans-esterification reactions in which the active site tyrosine of the enzyme becomes linked to the 5′-phosphate. An important advance in the understanding of the mechanism of topoisomerases IA has been made by the determination of the spatial structures of the Escherichia coli topoisomerase III (7Mondragon A. DiGate R. Struct. Fold. Des. 1999; 7: 1373-1383Abstract Full Text Full Text PDF Scopus (66) Google Scholar) and the 67-kDa fragment polypeptide from E. coli topoisomerase I (1Lima C.D. Wang J.C. Mondragon A. J. Mol. Biol. 1993; 232: 1213-1216Crossref PubMed Scopus (43) Google Scholar, 8Lima C.D. Wang J.C. Mondragon A. Nature. 1994; 367: 138-146Crossref PubMed Scopus (264) Google Scholar, 9Perry K. Mondragon A. Structure (Lond.). 2003; 11: 1349-1358Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar). This fragment, called Top67, contains the first 596 amino acids of the protein. It constitutes the core domain of E. coli topoisomerase I in which are present the totality of the conserved motifs, particularly those forming the active site of the protein (5Serre M.C. Duguet M. Prog. Nucleic Acid Res. Mol. Biol. 2003; 74: 37-81Crossref PubMed Scopus (13) Google Scholar, 10Kaltoum H. Portemer C. Confalonieri F. Duguet M. Bouthier de la Tour C. Syst. Appl. Microbiol. 1997; 20: 505-512Crossref Scopus (6) Google Scholar). The structural data combined with biochemical approaches have allowed us to postulate an enzyme-bridged mechanism for topoisomerases IA (11Kirkegaard K. Wang J.C. J. Mol. Biol. 1985; 185: 625-637Crossref PubMed Scopus (128) Google Scholar, 12Li Z. Mondragon A. DiGate R.J. Mol. Cell. 2001; 7: 301-307Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar, 13Dekker N.H. Rybenkov V.V. Duguet M. Crisona N.J. Cozzarelli N.R. Bensimon D. Croquette V. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 12126-12131Crossref PubMed Scopus (112) Google Scholar, 14Dekker N.H. Viard T. Bouthier de La Tour C. Duguet M. Bensimon D. Croquette V. J. Mol. Biol. 2003; 329: 271-282Crossref PubMed Scopus (25) Google Scholar). Like E. coli topoisomerase I, the enzyme from T. maritima can be divided into the following two domains: a core domain consisting of the first 540 amino acids of the protein, and a carboxyl-terminal domain consisting of the 93 remaining amino acids (Fig. 1). Whereas the core domains of bacterial topoisomerases I exhibit a high sequence similarity, the carboxyl-terminal domains are very divergent (5Serre M.C. Duguet M. Prog. Nucleic Acid Res. Mol. Biol. 2003; 74: 37-81Crossref PubMed Scopus (13) Google Scholar, 10Kaltoum H. Portemer C. Confalonieri F. Duguet M. Bouthier de la Tour C. Syst. Appl. Microbiol. 1997; 20: 505-512Crossref Scopus (6) Google Scholar, 15Bouthier de la Tour C. Kaltoum H. Portemer C. Confalonieri F. Huber R. Duguet M. Biochim. Biophys. Acta. 1995; 1264: 279-283Crossref PubMed Scopus (22) Google Scholar). They contain a variable number of zinc domains ranging from 0 to 5 (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar, 16Grishin N.V. J. Mol. Biol. 2000; 299: 1165-1177Crossref PubMed Scopus (47) Google Scholar). In E. coli topoisomerase I, there is a large carboxyl-terminal domain (268 amino acids) with three tetracysteine zinc-binding motifs (17Tse-Dinh Y.-C. Beran-Steed R.K. J. Biol. Chem. 1988; 263: 15857-15859Abstract Full Text PDF PubMed Google Scholar). Zinc deletion inactivates the enzyme (18Tse-Dinh Y.-C. J. Biol. Chem. 1991; 266: 14317-14320Abstract Full Text PDF PubMed Google Scholar), and mutation of one cysteine of the second zinc finger abolishes the cleavage specificity (19Zhu C.X. Qi H.Y. Tse-Dinh Y.C. J. Mol. Biol. 1995; 250: 609-616Crossref PubMed Scopus (21) Google Scholar). Moreover, the core domain Top67 is inefficient in DNA relaxation and can (1Lima C.D. Wang J.C. Mondragon A. J. Mol. Biol. 1993; 232: 1213-1216Crossref PubMed Scopus (43) Google Scholar). a of the zinc domain in the strand passage has been A. Tse-Dinh Y.C. Biochem. 2002; 3: PubMed Scopus Google Scholar). In T. maritima topoisomerase I, the of the 93 amino acids the carboxyl-terminal domain appears different from that of the E. coli we have that the hyperthermophilic enzyme contains a zinc that is not essential to the DNA relaxation activity and whose mutation not the or specificity of DNA cleavage (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar). In an to the respective roles of the carboxyl-terminal and core domains of the T. maritima topoisomerase I compared with those of E. we have and recombinant the two full-length topoisomerases I, an of T. maritima the two core TmTop65 and EcTop67, and three with the core domain of one protein to the of the and (Fig. 1). The different for various properties as follows: zinc to thermal stability, DNA cleavage efficiency, and The results of these a into the respective roles of the core and carboxyl-terminal domains in the mechanism of bacterial topoisomerases and for all T. maritima topoisomerase I T. maritima topoisomerase obtained as described (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar). DNA fragment the 540 first amino acids from T. maritima topoisomerase I prepared by DNA as DNA high and the following as the a site and as the a into the the and by DNA This the carboxyl-terminal of E. coli topoisomerase I to TmTop65 to a protein, the from the TmTop65 allow the of DNA full-length protein and from E. coli topoisomerase I E. coli topoisomerase I obtained by from DNA with as the an and as the a into the the DNA fragment the first 596 amino acids from E. coli topoisomerase I, also as (1Lima C.D. Wang J.C. Mondragon A. J. Mol. Biol. 1993; 232: 1213-1216Crossref PubMed Scopus (43) Google Scholar), also prepared with as the an and as the a the of This the carboxyl-terminal domain of T. maritima topoisomerase I to to the protein the from the other DNA the and amino acids from E. coli topoisomerase I by as and a For the as the a then the of TmTop65 the The from these chimera the fragment to the amino acids from I and chimera the fragment to the amino acids of I DNA fragment the 93 amino acids from I obtained by the two as the a and as the a This fragment the of DNA The protein chimera a of the the and two amino one and one the into E. coli of and °C in with and the of with for and the and °C of obtained from of The to all the recombinant in of by and for to the to a of for the for to the and the allowed to °C for The in of and this The by for and an with A. with and the by a from to a consisting of They and in an a with to a of to of the active by the of and C. Biochem. PubMed Scopus Google Scholar) with as a or by the of recombinant protein. Zinc zinc of the type and by a of in of to a of a enzyme Zinc from the enzyme by the of the whose is A. Biochem. 1985; PubMed Scopus Google Scholar). DNA and of negatively supercoiled DNA The by the protein to be which in a The protein to the of of °C, the by of and through in for 5 with and °C for different to and for their DNA relaxation activity as described a cleavage site for the T. maritima topoisomerase I by the (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar), and by to or of this 5 of in the presence of of in of as by the of °C, the by the 75 °C for This allowed us to the of topoisomerase I to with the of the in the trans-esterification mechanism of type IA the tyrosine of the active site a covalent with the of the strand, the which to the protein. The size following the For of the with of in the presence of of in of as by the of °C, the by the to °C for 5 and of the with of protein in and for °C in a of The then as follows: to of a and 5 a °C for and to the The second of the by the of and of The by °C for and an in The for and to the In (Fig. the a of a as described and the remaining with and °C for to the of of the with of protein in for °C in a of The by of of and The °C for and a the to for the of T. maritima and E. coli the respective roles of the core and carboxyl-terminal in the mechanism of the T. maritima topoisomerase I compared with that of E. (Fig. 1). a composed of the first 540 amino acids of the T. maritima from sequence with other bacterial topoisomerases I H. Portemer C. Confalonieri F. Duguet M. Bouthier de la Tour C. Syst. Appl. Microbiol. 1997; 20: 505-512Crossref Scopus (6) Google Scholar). It to the trans-esterification domain of the protein and all the conserved motifs present in the The core domain of E. coli topoisomerase I first 596 amino called Top67, whose structure is C.D. Wang J.C. Mondragon A. Nature. 1994; 367: 138-146Crossref PubMed Scopus (264) Google Scholar), also and into the as the other The polypeptide these in to with The three then In the the entire carboxyl-terminal of E. coli topoisomerase I amino acids) the three zinc to the two first zinc in E. coli I described as essential for a second chimera in which a sequence the zinc finger and the of the carboxyl-terminal domain of E. coli I amino acids) to to for a of the E. coli Top67 fragment by the carboxyl-terminal of T. maritima topoisomerase I, a protein, in which the entire carboxyl-terminal sequence of T. maritima topoisomerase I 93 to and Zinc of the in E. coli and as described as follows: the two full-length E. coli and T. maritima topoisomerases I, the T. maritima in which the tyrosine involved in the trans-esterification has been by a (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar), and the by They the size and (Fig. For the E. coli we a a also obtained in other but not appear to properties S. Z. H. DiGate R.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the of zinc on the activity of E. coli topoisomerase We the of the various to zinc The zinc by the This is to from zinc-binding by of a on cysteine A. Biochem. 1985; PubMed Scopus Google Scholar). zinc is then by the The in that in all the recombinant in E. coli have the number of zinc in their structure as follows: three zinc are to the full-length E. coli enzyme and the one zinc for full-length T. maritima and and zinc for TmTop65 and T. maritima I (TmTop65) core domain of E. coli topoisomerase I contains all the conserved motifs found in topoisomerases IA but the to relaxation (1Lima C.D. Wang J.C. Mondragon A. J. Mol. Biol. 1993; 232: 1213-1216Crossref PubMed Scopus (43) Google Scholar, Wang J.C. J. Mol. Biol. PubMed Scopus Google Scholar). This us to the relaxation activity of the T. maritima topoisomerase deletion to in the activity of TmTop65 is about compared with the full-length enzyme the temperature of This the of the carboxyl-terminal domain for enzyme by DNA binding efficiency binding of recombinant topoisomerases of the with of full-length I, I, and and and and topoisomerases as described The reactions and through a enzyme in the control The that TmTop65 relaxation activity (Fig. and 0 In the is as described (1Lima C.D. Wang J.C. Mondragon A. J. Mol. Biol. 1993; 232: 1213-1216Crossref PubMed Scopus (43) Google Scholar). This that the core domain TmTop65 of T. maritima is able to complete topoisomerization strand passage and religation the temperature for T. maritima topoisomerase is 75 °C, we also the activity of TmTop65 this temperature and found that is 75 °C and of the The results obtained with TmTop65 us to the of the recombinant enzymes that we have of 75 °C the T. maritima full-length topoisomerase I (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar). We then the relaxation of all the °C and their °C for various The results are in The first is that the and the hyperthermophilic full-length topoisomerases exhibit relaxation °C, although the is At high of the E. coli topoisomerase I with the T. maritima The second is that of the carboxyl-terminal and has on their activity and stability, the of these domains for activity. The question we addressed the of a carboxyl-terminal domain to the core with fusion of the complete carboxyl-terminal of the E. coli I an important activity the appears to be about more active In °C is is active a this TmTop65 is 5 with the relaxation activity and results that the carboxyl-terminal domain of E. coli topoisomerase I is to and a core We have also the of the carboxyl-terminal of T. maritima, to the EcTop67, to activity. in a relaxation activity °C for this The activity 5 °C, but the activity is low to DNA This that the core can be by the carboxyl-terminal domain of T. maritima topoisomerase The activity in this the in DNA binding The of on the of a the carboxyl-terminal of E. coli and T. maritima topoisomerases appear essential to or the DNA relaxation we the different steps of the topoisomerization cycle. The first is the binding of the enzymes to DNA. For this a the described as a a site for T. maritima topoisomerase I (4Viard T. Lamour V. Duguet M. Bouthier de la Tour C. J. Biol. Chem. 2001; 276: 46495-46503Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar) and in T. maritima and E. coli topoisomerases the a with low in a The of the is the as in the of the of T. maritima which is to the (Fig. This is that although the active recombinant enzymes the the DNA in the is the for DNA of the carboxyl-terminal and TmTop65 in on binding (Fig. This that the for the low activity or the complete of activity for TmTop65 and EcTop67, is the binding or the of binding to the DNA We the of a carboxyl-terminal domain to the binding of the core This is for the chimera the of the carboxyl-terminal domain of E. coli topoisomerase to TmTop65 binding (Fig. as for DNA the chimera although a is obtained (Fig. of a low of binding also in the chimera the carboxyl-terminal of T. maritima to (Fig. these results that the of binding of recombinant to DNA the DNA relaxation activity described Thus, binding to an that constitutes the first of the topoisomerization cycle, is an important for activity and is by the carboxyl-terminal domain of the recombinant The TmTop65 and E. coli E. coli I the of the different enzymes to DNA and the specificity of of the in on a The results are in of the the are able to the although with different and the full-length enzymes I and I exhibit a cleavage with cleavage and for in their specificity appears to be I the I (Fig. of the carboxyl-terminal the cleavage and the cleavage (Fig. TmTop65 and TmTop65 and with low efficiency. This specificity that the of the core domains TmTop65 and on the is different from that of the full-length topoisomerases with their carboxyl-terminal the of a in of the cleavage Cozzarelli N.R. J. Biol. Chem. 1985; Full Text PDF PubMed Google Scholar, Nucleic Res. PubMed Scopus Google Scholar, C. Duguet M. M. J. Biochem. 1999; PubMed Scopus (21) Google Scholar) is in all The cleavage obtained with the are For the the cleavage for to the of two other as follows: a site to that found for the full-length E. coli topoisomerase I and a site to that found for the full-length T. maritima topoisomerase I This that the carboxyl-terminal of E. coli topoisomerase I contains to the specificity of DNA Moreover, this carboxyl-terminal domain appears to allow two different of the enzyme on the is the by E. coli topoisomerase I, and the more is the as the by the carboxyl-terminal of T. maritima topoisomerase. For the of the cleavage that the specificity of This to the of the two first zinc present in for cleavage The and the T. maritima to the by the cleavage obtained with the the carboxyl-terminal of T. maritima is to Moreover, cleavage all different from those described (Fig. and of the (Fig. This with the very low of binding to the that to An be that the of DNA religation of this chimera is very in such a that the of the is not by the protein. this we the reactions for the of 5 on a more to the or by and on the The results are in I, I, and the chimera with the with and to the of DNA the of to cleavage in the is different in the of the for which the (Fig. This by and (Fig. results that, contrary to the other topoisomerase is not able to the cleavage to the of the This be the of cleavage on the and the question of covalent binding to the on the of the covalent by the the and the of the to the by (Fig. the appears with the full-length E. coli and T. maritima I, as as with in the of covalent adduct to the of a activity of the In we that the by are with are the cleavage by I and In fragment by on a this a The described in this allow a understanding of the respective roles of the two domains in bacterial topoisomerases I as follows: the highly conserved core also trans-esterification and the more divergent carboxyl-terminal E. coli and T. maritima domains and for their to and DNA. The results are in of the results obtained with the different recombinant in a The first is the of the carboxyl-terminal domain of T. maritima topoisomerase I to high relaxation activity. Thus, this domain of 93 amino acids a to the large carboxyl-terminal domain of the E. coli An that the core enzyme TmTop65 of T. maritima is able to relaxation of supercoiled although with low efficiency. relaxation activity that the protein the following steps in a topoisomerization binding to strand and The of relaxation activity on the the low binding efficiency with TmTop65 the low activity of cleavage and that the is the first binding to DNA. of the carboxyl-terminal of E. coli I to TmTop65 increases binding and relaxation activity by about Thus, we that the core TmTop65 domain is of a complete of strand and that the efficiency of the is highly on binding to DNA The question this can be to the core domains of other bacterial topoisomerases In the of E. DNA binding and relaxation activity fusion of to the carboxyl-terminal domain of It is that this domain is with the for the full-length T. maritima topoisomerase I, the carboxyl-terminal domain with core domain high DNA binding and relaxation activity. This of the carboxyl-terminal of T. maritima topoisomerase I from the generally one of a carboxyl-terminal a in DNA strand the core domain in of the Y.-C. Biochim. Biophys. Acta. 1998; 1400: 19-27Crossref PubMed Scopus (51) Google Scholar, A. Tse-Dinh Y.C. Biochem. 2002; 3: PubMed Scopus Google Scholar). The by the cleavage a of the carboxyl-terminal of the in the of the enzymes on DNA. the cleavage obtained with the that the carboxyl-terminal of E. coli topoisomerase I (268 amino acids) is able to the cleavage specificity of the full-length E. coli enzyme to the core domain The of a cleavage to the specificity of the full-length T. maritima topoisomerase I two of of the topoisomerase on the for an important of the carboxyl-terminal domains in is that cleavage of the core domains TmTop65 and are different from those of the full-length results the of the carboxyl-terminal in the mechanism of E. coli topoisomerase I are not with our has been that the in one of the three zinc in the carboxyl-terminal of the protein, cleavage site specificity (19Zhu C.X. Qi H.Y. Tse-Dinh Y.C. J. Mol. Biol. 1995; 250: 609-616Crossref PubMed Scopus (21) Google Scholar). our from that of A. Tse-Dinh Y.C. Biochem. 2002; 3: PubMed Scopus Google Scholar) that E. coli Top67 the sequence and structure for DNA cleavage as the full-length We this although be to the nature of with the topoisomerase in which the E. coli topoisomerase I of the second zinc finger is to that the of the carboxyl-terminal is important for binding and the low and low relaxation to Moreover, the specificity of cleavage that of results the of the two first zinc in the of the E. coli carboxyl-terminal The results obtained with the chimera fusion of the carboxyl-terminal of I to binding and relaxation a high of cleavage and that, contrary to the other the In this appears that the are on the on the a very low of the enzyme is in a for the relaxation with can be for the The covalent formed with are to a that is to the chimera or the of cleavage on the that of the contains a the data in the this an of DNA this activity belongs to or to a is not important the of the E. coli carboxyl-terminal domains to to This can be compared with the high of the full-length I carboxyl-terminal An of the carboxyl-terminal in topoisomerases IA is to allow the protein to into a more and this is essential for a topoisomerase. The two domains have to be the This in the of I by the to by the presence of the carboxyl-terminal of the R. M. and C. Bouthier de La Taken together, the of the present us to that the trans-esterification domain of topoisomerases IA is able to complete topoisomerization with low efficiency and low The of the carboxyl-terminal domain can be compared with that of an domain for the core domain, considerably binding efficiency to DNA and more these can be to the entire topoisomerase IA family is a We M. C. for critical of the with