>TIGR01051 topA_bact DNA topoisomerase I; InterPro: IPR005733 DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks. These enzymes have several functions: to remove DNA supercoils during transcription and DNA replication; for strand breakage during recombination; for chromosome condensation; and to disentangle intertwined DNA during mitosis , . DNA topoisomerases are divided into two classes: type I enzymes (5.99.1.2 from EC; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (5.99.1.3 from EC; topoisomerases II, IV and VI) break double-strand DNA . Type I topoisomerases are ATP-independent enzymes (except for reverse gyrase), and can be subdivided according to their structure and reaction mechanisms: type IA (bacterial and archaeal topoisomerase I, topoisomerase III and reverse gyrase) and type IB (eukaryotic topoisomerase I and topoisomerase V). These enzymes are primarily responsible for relaxing positively and/or negatively supercoiled DNA, except for reverse gyrase, which can introduce positive supercoils into DNA. This entry describes topoisomerase I from bacteria, which is more closely related to archaeal than to eukaryotic topoisomerase I . Topoisomerase I is the major enzyme for relaxing negatively supercoiled DNA, and its presence is balanced by reverse gyrase, which can introduce negative supercoils. Prokaryotic topoisomerase I folds in an unusual way to give 4 distinct domains, enclosing a hole large enough to accommodate a double-stranded DNA segment. A tyrosine at the active site, which lies at the interface of 2 domains, is involved in transient breakage of a DNA strand, and the formation of a covalent protein-DNA intermediate through a 5-phosphotyrosine linkage. The structure reveals a plausible mechanism by which this and related enzymes could catalyse the passage of one DNA strand through a transient break in another strand . Topoisomerase I require Mg2+ as a cofactor for catalysis to take place. More information about this protein can be found at Protein of the Month: DNA Topoisomerase .; GO: 0003677 DNA binding, 0003917 DNA topoisomerase type I activity, 0006265 DNA topological change, 0006268 DNA unwinding during replication, 0005694 chromosome.

Probab=100.00 E-value=0 Score=1744.40 Aligned_cols=632 Identities=46% Similarity=0.764 Sum_probs=585.3 Q ss_pred EEEECCHHHHHHHHHHHCCCCEEEEEECCCEECCCC------------------CCCCCCCCC--CCEEEEECCCHHHHH Q ss_conf 899779047877887508998999942511007865------------------578676667--440688776548999 Q gi|254780306|r 3 VIIVESPAKAKTISKYLGSNYKVLSSFGHIRDLPAK------------------KGSVLPEKE--FEMIWNIDPSSQKHL 62 (837) Q Consensus 3 LvIvEsP~kak~I~~~Lg~~y~V~as~GHirdLp~~------------------~~~v~~~~~--f~p~y~v~~~~kk~~ 62 (837) T Consensus 1 LVIVESPAKAKTI~~YLG~~Y~V~aS~GHiRDLP~sa~~~~~~yk~~~rGa~wa~lGvd~e~~~qF~P~Y~~~~~K~~~V 80 (688) T TIGR01051 1 LVIVESPAKAKTIKKYLGKEYEVEASMGHIRDLPKSASDVPEKYKSQERGALWARLGVDIEKNKQFEPEYVVSKGKKKVV 80 (688) T ss_pred CEEEECCHHHHHHHHHCCCCCEEEEECCCHHHCCCHHHCCCHHCCCCCCCCEEECCCCCCCCCCCCCCCEEECCCHHHHH T ss_conf 95872453899998648998689972385221020001044320787343222024543213784165043546144789 Q ss_pred HHHHHHHHHCCEEEECCCCCCHHHHHHHHHHHHHHHHCCCCCCCEEEEEEECCCHHHHHHHHHCCCCCCHHHHHHHHHHH Q ss_conf 99999987099899946997025799999999975512578871699998037989999998622646989999999999 Q gi|254780306|r 63 QNIIHAVKSSTILILATDPDREGEAISWHVLDVLRQKNLIEKTKIQRVSFNAITKQVVLNAMKSPRDINLDLVNAYLARR 142 (837) Q Consensus 63 ~~i~~~~k~a~~iilAtD~DREGE~Iawhi~e~l~~~~~~~~~~v~R~~f~eiT~~aI~~A~~n~r~~d~~Lv~A~~aRr 142 (837) T Consensus 81 ~~L~~lakkA~~~yLAtD~DREGEAIaWHl~~~l~~~~~~~ddf~kR~VFnEIT~~AI~~A~~~PR~ID~~~V~AQ~ARR 160 (688) T TIGR01051 81 KELKTLAKKADEVYLATDPDREGEAIAWHLAELLKPKLKVKDDFYKRIVFNEITKKAIRAALKNPREIDMNLVNAQQARR 160 (688) T ss_pred HHHHHHHHHCCEEEECCCCCCCHHHHHHHHHHHHCCCCCCCCCCCCCEECCCCCHHHHHHHHHCCCCCCHHHHHHHHHHH T ss_conf 99999987316156404888540258999999807546775643065002476778999998377202435688887765 Q ss_pred HHHHHHHHHHCHHHHHHCCCCCCCCCHHHHHHHHHHHHHHHHHHCCCCCCEEEEEEEECCC------CCEEEEEEEEECC Q ss_conf 9898740113789886414676534226899999999999964137654400122331579------9654223310358 Q gi|254780306|r 143 ALDYLVGFNLSPILWQKLPGARSAGRVQSVALRLICNRENQIESFVSEEYWSLSVLLETPR------NDKFTAHLTDFNG 216 (837) Q Consensus 143 ~lD~lvG~~lSp~L~rk~~~~lSaGRVQtp~L~lIveRe~eI~~F~p~~y~~i~a~~~~~~------~~~f~a~l~~~~~ 216 (837) T Consensus 161 iLDRlVGY~lSPlLW~K~~~gLSAGRVQSVAlRLi~~RErEi~~Fvp~~YW~~~~~~~~~~~~~~~~~~~f~A~l~~~~g 240 (688) T TIGR01051 161 ILDRLVGYKLSPLLWKKVAKGLSAGRVQSVALRLIVDREREIKRFVPEEYWTVDAKLEAKNNQKVACKETFEALLTEVNG 240 (688) T ss_pred HHCEEEEEEECHHHHHHCCCCCCCCCHHHHHHHHHHHHHHHHHHCCCCCEEEEEEEEECCCCCCCHHHHCCCCEEEEECC T ss_conf 62122210575347731236787760565567677754789861688611798999645666311111046321241247 Q ss_pred EEECCCC----------------HHHHHHHHHHHHHHCCCCCEEEEEECCCCCCCCCCCCCHHHHHHHHHHHHCCCHHHH Q ss_conf 3303310----------------113566677764200156301000023322246852103799999887608889999 Q gi|254780306|r 217 QRIEKKS----------------ISNKKEADDLISFVKKATYSVEKIENKPIKRNPWPAFTTSTLQQVASSRLGFSASHT 280 (837) Q Consensus 217 ~~~~~~~----------------~~~~~~a~~~~~~~~~~~~~V~~v~~k~~~~~Pp~Pf~tstLQq~As~~lg~sa~~T 280 (837) T Consensus 241 ~kl~~~~~~D~~~g~l~~G~~v~~L~E~~A~~~~~~L~~~~~~V~~~e~K~~~~~P~~PF~TSTLQQeA~~KLGFSa~kT 320 (688) T TIGR01051 241 KKLKAGSDFDPLTGELRPGKEVVVLNEAEATALKEQLKGEEYVVEEIEKKPKKSRPPPPFTTSTLQQEASRKLGFSAKKT 320 (688) T ss_pred CCCCCCCCCCCCCCCCCCCCEEEEECHHHHHHHHHHCCCCEEEEEEEECCCCCCCCCCCCCCCHHHHHHHHHCCCCCCHH T ss_conf 01132124780101268997168818699999998507864799886304330176348335418998877537951026 Q ss_pred HHHHHHHHCCCCCCCHHHHHHHHCCCCCCCCCHHHHHHHHHHHHHHCCCCCCCCCC--CCCCCCCCCCCCCCCCEEEE-E Q ss_conf 99998762135567212245531475544443056899997655200112376311--11255666887776524773-0 Q gi|254780306|r 281 MRIAQKLYEGIDVNGEIVGLITYMRTDGVHMSPDALEAVRRSITSHYGDHYLPEKP--RIYSSKSKNAQEAHEAIRPN-D 357 (837) Q Consensus 281 m~iAQ~LYE~~~~~~~~~GlITYpRTDS~~ls~ea~~~~r~~i~~~~g~~~l~~~~--r~y~~k~k~aQeAHeAIrPT-~ 357 (837) T Consensus 321 M~iAQ~LYEGv~~~~~~~G~ITYMRTDS~~lS~~A~~eaR~~I~~~yG~~YL~~~~kLk~y~~k~KnaQeAHEAIRPtG~ 400 (688) T TIGR01051 321 MMIAQRLYEGVSLGEGTVGLITYMRTDSTRLSNEAVNEARNLIDKNYGKEYLGPKPKLKRYKSKEKNAQEAHEAIRPTGS 400 (688) T ss_pred HHHHHHHHCCEECCCCEEEEEECCCCCCHHHHHHHHHHHHHHHHHHCCHHCCCCCCCCCCHHHCCCCCCCHHHCCCCCCC T ss_conf 55542331254438955899832863305789999999998888621120378874223102216875001104476431 Q ss_pred CCCCCCHHCCCCCH---HHHHHHHHHHHHHHHHHHHHHEECCCEEEEEEEECCCEEEEEEEEEEEECCCHHHHHCCCCCC Q ss_conf 23464000001999---999999999999999852221100100136774079639999987488058856763267776 Q gi|254780306|r 358 FDFLPSKMKQFLDS---DQFQLYNLIWKRSVASQMASAKFERTTVNIIATYNDQIGHLRTTGSLLCFDGFLKVWENQYDQ 434 (837) Q Consensus 358 ~~~~p~~~~~~L~~---de~klY~LI~~R~lasqm~~a~~~~~~v~i~~~~~~~~~~F~asg~~i~~~G~~~vy~~~~~~ 434 (837) T Consensus 401 ~~~tP~~lk~~L~~PniD~~rLY~LIW~RfVASQM~dA~~~~~~v~l~~~~g~~~~~F~A~g~~~~FdGf~kvy~e~~dd 480 (688) T TIGR01051 401 VFRTPEELKAELKRPNIDELRLYELIWKRFVASQMADARYDSLSVRLTAEKGSVEVVFKASGRKLLFDGFYKVYVEGSDD 480 (688) T ss_pred EEECHHHHHHHCCCCCHHHHHHHHHHHHHHHHHCCCCCCEEEEEEEEEEECCCEEEEEEEECCEEECCHHHHHHHCCCCC T ss_conf 10174888522377566788888999999887448775326899999861374015897402356455236664127887 Q ss_pred CCC--CHHHCCCCCCCCCCCCCCEEEECCCCCCCCCCCCCHHHHHHHHHHCCCCCCCCHHHHHHHHHHCCEEECCCCCEE Q ss_conf 321--001014886456882110011011123464310178998743321025665515789999973220221477122 Q gi|254780306|r 435 EKN--SEEDILLPYISANEQLIATETNASQHFTEPPPRYSESSLIKKMEEIGIGRPSTYATILETLYKRKYVIAEKRKIL 512 (837) Q Consensus 435 ~~~--~~~~~~LP~l~~g~~~~~~~~~~~~~~TkPP~rytEasLik~mE~~GIGrPSTyA~II~~L~~R~YV~~~~~~l~ 512 (837) T Consensus 481 ~~~alee~~~~LP~Lk~Gd~~~~~~~~~~~H~T~PPaRYTEASLVK~LE~~GIGRPSTYAsiis~iqdRgYv~~~~k~l~ 560 (688) T TIGR01051 481 DDEALEEKDRILPPLKEGDAVKLVEVEPNQHFTQPPARYTEASLVKELEELGIGRPSTYASIISTIQDRGYVKLENKRLV 560 (688) T ss_pred HHHHHCCCCCCCCCCCCCCEEEEEECCCCCCEECCCCCCCHHHHHHHHHHCCCCCCCCHHHHHHHHHCCCEEEEECCCCC T ss_conf 16752224577878888862002752314510182798652479999985778899725558867506520330244002 Q ss_pred ECCHHHHHCCCCCCCCCCCCCHHHHHHHHHHHHHHHCCCHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHCC Q ss_conf 20114200002233665568988999999999998626013478999986767665576677556667765567664102 Q gi|254780306|r 513 PQNTGRIVTAFLENFFSQYVEYDFTADLEEKLDEISTGKLNWKEVLHEFWEEFIEKIDSIKKLRISNVLDILNDTLSSVI 592 (837) Q Consensus 513 pT~~G~~v~~~L~~~f~~~~~~~fTa~~E~~ld~Ia~G~~~~~~~L~~Fy~~f~~~i~~~~~~~~~~v~d~l~~~~~~~~ 592 (837) T Consensus 561 p~~~g~~V~~~Le~hF~~~Vd~~FTA~ME~~LDeiA~gk~~w~~~L~~Fy~~F~~~v~~~~~~~~a~~~---~~~~~~~~ 637 (688) T TIGR01051 561 PTELGFAVTDLLEKHFGELVDYDFTAKMEKELDEIAEGKAEWKPVLKNFYTGFSSKVEKVVEQKIALKD---LVERKMRE 637 (688) T ss_pred HHHHHHHHHHHHHHHCCCCCCCHHHHHHHHHHHHHHCCCHHHHHHHHHHCCCCCCCCCHHHHHHHHHHH---HHHHCCCC T ss_conf 027789999998864264335502376434467885051567999961068603454224543102224---56300013 Q ss_pred CCCCCCCCCCEECCCCCCCCEEEEEECCCC--CCCCCCCCC---CCCCCCCC Q ss_conf 455556766114334677731368715776--111234343---23332100 Q gi|254780306|r 593 FPPKENNEDSRTCPECHTHSLSLKLSSKYG--AFVGCTNYP---ECKYTRQL 639 (837) Q Consensus 593 ~~~~~~~~~~~~Cp~C~~g~L~~k~~gK~G--~FigCSnyP---eCk~t~~l 639 (837) T Consensus 638 ~~~~~~~~~~~~C~~Cg~-~~~~k-~Gk~Gne~fl~Cs~~P~~~~C~~~~~~ 687 (688) T TIGR01051 638 IDDKEKEKTSKDCPLCGS-PMVVK-LGKYGNEPFLACSNFPEKEKCKLTKSI 687 (688) T ss_pred CCCCCCEECCCCCCCCCC-EEEEE-ECCCCCHHHHCCCCCCCCCCCCCCCCC T ss_conf 311220001443534687-13686-303577254317831570206877788

HHsearch alignment for GI: 254780306 and conserved domain: TIGR01051