The following text describes a protein:
Function:
Modifies the topological state of DNA by introducing positive supercoils in an ATP-dependent process, increasing the linking number in steps of +1. Very efficient supercoiling occurs on relaxed DNA with a single-stranded bubble; the minimal bubble is 20 nucleotides (nt) and up to 10 positive supercoils can be introduced into a 3.1 kb plasmid with a 50 nt bubble. Positively supercoils DNA with all (d)NTPS, although it requires about 10-fold more of non-(d)ATP. In the absence of ATP (or at low levels of enzyme), or in the presence of ADP, relaxes negative supercoils. Only relaxes positive supercoils when the substrate contains a bubble. Also promotes strand annealing of complementary ssDNA circles. Binds to single-stranded DNA, transiently cleaves and then rejoins the ends, introducing a positive supercoil in the process. The scissile phosphodiester is attacked by the catalytic tyrosine of the enzyme, resulting in the formation of a DNA-(5'-phosphotyrosyl)-enzyme intermediate. Probably involved in rewinding DNA strands in regions of the chromosome that have opened up to allow replication, transcription, DNA repair and/or for DNA protection (Probable); In vitro protects DNA against degradation at 90 degrees Celsius, reducing dsDNA breakage about 8-fold; ATP hydrolysis is not necessary, while ADP decreases the protection somewhat. Coats all forms of dsDNA; the DNA is protected against cleavage and transcription. Recognizes nicked DNA and forms a coat at the nicking site, which may help hold DNA in a structure amenable to repair.
Miscellaneous:
MISCELLANEOUS: This enzyme is the only unique feature of hyperthermophilic bacteria/archaea known and seems to be essential for adaptation to life at high temperatures. It may play a role in stabilization of DNA at high temperatures.
Subcellular Localization:
Cytoplasm.
Domain:
Introduction of positive supercoils requires the cooperation of both domains. The helicase-like domain probably does not directly unwind DNA, but more likely acts by driving ATP-dependent conformational changes within the whole enzyme. A beta hairpin in the 'latch' region of the N-terminal domain plays a regulatory role in the enzyme, repressing topoisomerase activity in the absence of ATP and preventing the enzyme from acting as an ATP-independent relaxing enzyme; it also helps to coordinate nucleotide hydrolysis by the ATPase domain with the supercoiling activity of the topoisomerase domain.
Sequence:
MIPVVYSNLCPVCGGDLESKEIEKHVCFRKKRSLCLFPEDFLLKEFVEFFRKCVGEPRAIQKMWAKRILRKESFAATAPTGVGKTSFGLAMSLFLALKGKRCYVIFPTSLLVIQAAETIRKYAEKAGVGTENLIGYYHGRIPKREKENFMQNLRNFKIVITTTQFLSKHYRELGHFDFIFVDDVDAILKASKNVDKLLHLLGFHYDLKTKSWVGEARGCLMVSTATAKKGKKAELFRQLLNFDIGSSRITVRNVEDVAVNDESISTLSSILEKLGTGGIIYARTGEEAEEIYESLKNKFRIGIVTATKKGDYEKFVEGEIDHLIGTAHYYGTLVRGLDLPERIRFAVFVGCPSFRVTIEDIDSLSPQMVKLLAYLYRNVDEIERLLPAVERHIDEVREILKKVMGKERPQAKDVVVREGEVIFPDLRTYIQGSGRTSRLFAGGLTKGASFLLEDDSELLSAFIERAKLYDIEFKSIDEVDFEKLSRELDESRDRYRRRQEFDLIKPALFIVESPTKARQISRFFGKPSVKVLDGAVVYEIPMQKYVLMVTASIGHVVDLITNRGFHGVLVNGRFVPVYASIKRCRDCGYQFTEDRESCPKCGSENVDNSRSRIEALRKLAHDAEFVIVGTDPDTEGEKIAWDLKNLLSGCGAVKRAEFHEVTRRAILEALESLRDVDENLVKAQVVRRIEDRWIGFVLSQKLWERFNNRNLSAGRAQTPVLGWIIDRFQESRERRKIAIVRDFDLVLEHDEEEFDLTIKLVEEREELRTPLPPYTTETMLSDANRILKFSVKQTMQIAQELFENGLITYHRTDSTRVSDVGQRIAKEYLGDDFVGREWGESGAHECIRPTRPLTRDDVQRLIQEGVLVVEGLRWEHFALYDLIFRRFMASQCRPFKVVVKKYSIEFDGKTAEEERIVRAEGRAYELYRAVWVKNELPTGTFRVKAEVKSVPKVLPFTQSEIIQMMKERGIGRPSTYATIVDRLFMRNYVVEKYGRMIPTKLGIDVFRFLVRRYAKFVSEDRTRDLESRMDAIERGELDYLKALEDLYAEIKSID