The following text describes a protein:
Function:
Modifies the topological state of DNA by introducing positive supercoils in an ATP-dependent process (Probable). Increases the linking number in steps of +1. Involved in homeostatic control of DNA topology in balance with type II topoisomerase 6 (TopoVI); levels of TopoVI are constant at 80 and 88 degrees Celsius and TopoVI is probably less active at 88 degrees (characterized enzyme is from S.shibatae B12), so reverse gyrase mediates most of the fine-tuning of DNA topology. Changes the DNA linking number step-by-step in a distributive manner. At low protein to DNA ratios mostly relaxes negatively supercoiled substrate, as ratios rise more positive supercoils are introduced. At 90 degrees Celsius introduces 19 positive supercoils into pTZ18R DNA (probably 2860 bp), less than TopR2. Relaxes negatively supercoiled DNA in the absence of ATP. It cleaves transiently a single DNA strand and remains covalently bound to the 5' DNA end through a tyrosine residue (Probable). May be involved in DNA damage response (Probable). Its activity is inhibited by the DNA-binding protein 7d (Sso7d), suggesting that the Sso7d activity might counteract the overwinding effect of reverse gyrase (By similarity); Resolves 4-way Holliday junctions (HJ) with 20 bases in each arm in vitro, distorting the junction. Very high protein levels are required, but total enzyme content of the cell (there are 2 reverse gyrases in this organism) is estimated to be 20-200 molecules/cell. HJ resolution does not require either ATPase activity or the active tyrosine. The individual domains do not resolve HJs but do so when mixed. Also unwinds a fork substrate; There are 2 genes for this protein in the cell. During exponential growth this is the less expressed isoform (about 52 molecules per cell at 80 degrees Celsius, about 28 molecules at 88 degrees Celsius); this isoform is more active at higher temperature. Grows actively at both 80 and 88 degrees Celsius; survives a long exposure at 45 degrees Celsius without DNA replication or cell division occurring. Experiments using whole cell extracts do not distinguish which isoform is present, the results are probably a mixture of the two forms (Probable).
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. Note=Upon UV irradiation up to 60% of the reverse gyrase activity becomes associated with DNA in vivo.
Domain:
Both the DNA unwinding and positive supercoiling activities require the cooperation of both domains. The cooperative action between the helicase-like and the topoisomerase domains is specific. The helicase-like domain probably does not directly unwind DNA but acts more likely by driving ATP-dependent conformational changes within the whole enzyme, functioning more like a protein motor. The 'latch' region of the N-terminal domain plays a regulatory role in the enzyme, repressing topoisomerase activity in the absence of ATP and therefore 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:
MTSINKVPPSIYTRSCPNCGGNISSQRLFNGSVCESCLKDDREFSNLSDLINILSENSNLKNLTQIRDVLEEYKKVEEIFGKLLNNSKPIGPQRSWTIRFLRGESFAIIAPPGLGKTTFGLIMSLYNATRNRKSIIIFPTRTLISQTVDKLAKFSELYSYSPRILYNKQSPTQTENILDQLKSGNFDIFISTNRFVIQNLSELSNIKFDFIFVDDVDAALKSGKSAKAILRLVGFTDEDIQTTMKLLRENIGEEEKFGKIQEIRESRLKDKIVIFSSATISRGNPILSSLMGFRPGSSVIYLRNIYDSYIDLTQTCKGQDFEECTLGTVIKLLKRLNDGTLIFVPIDKGAQYADYLASNLRDHGINVESVASSSISKLEKFERGEVSSLVGVATHYGVLVRGIDLPWRVKYSIFVGIPKFKFKIGEYMHPLALTRLLSLVYLVKNDDKVRGLLSYIRKRLRKISPAALAMLAKDIREGKIDDERLKEAYNLVNEYLKDNEFLKKVSDVGDLVIEGDYILMPDYLTYIQASGRTSRLYGANLTTGLSVLLIDNSRLFELLNKKLNLILDEVKWYSLDIDADKLGQVSLSDISAKITEERESLSKIKKEGNVESSSLSVKTTLFIVESPNKAKTISNFFSRPSTRSYGKLRVYETVLGDRVLIVAASGGHIYDLITEDESEKQDDNYVYGVLVKDSKFIPIYSTIKKCEKGHQIVKDLSQNKCPICGSRIVTDKTEVVDILRKLALEVDEVLIGTDPDTEGEKIAWDIYLAIRPFNGNIKRAEFHEVTRRAILNAIKNPREFNDNLVKSQIVRRIEDRWIGFKLSRKLQTEFWEQHCTSISKKNSKDEECKENRNLSAGRVQTPVLDWVVNRYQKYNENKKKYLIIESQDKSIFPFSVLALKKNGLSKNTQIIIHLEDINIKEEEFGPLPPYTTDTLLSDAANLLRIPASDTMRVAQDLFELGLITYHRTDSTRVSNVGISVAETYLKSKQVDISKIFRPRSWGEGGAHEAIRPTKPLDETMLKASIEQGDLELSKQLTFNHFRVYNLIFRRFITSQLPPLVVTKQIVRIRAYTKDNIELELDENKKEFVIGYKLKEGDEFRQTLQDAIYTLFRLYQPLDEKMKGKELSATITGTLNKSDVQLYTEGELISEMKSKQIGRPSTYAVIISTLKKRRYIIESKNLKKIIPTKLGMAVKEYLMENYKQIVSEKRTVKLLEKMNEVEEGKVDYLVLLKELYNEIQTIS