Dissertations / Theses on the topic 'Type II topoisomerase'

Thesis (Ed. D.)--Illinois State University, 1990.
Title from title page screen, viewed November 28, 2005. Dissertation Committee: Herman E. Brockman (chair), Alan J. Katz, Lynne A. Lucher, Radheshyam K. Jayaswal, David F. Weber, Anthony E. Liberta. Includes bibliographical references (leaves 114-131) and abstract. Also available in print.

uinolones are a family of drugs used to treat bacterial infections by targeting bacterial type II topoisomerases (TOP2s), DNA gyrase and topoisomerase IV. Recent studies have shown that quinolones can cause genotoxicity in mammalian cells. Genotoxicity occurs when an agent causes damage to the genetic apparatus of a cell. Due to the similarities between the mammalian and bacterial TOP2 enzymes it is thought that the quinolones are targeting mammalian TOP2 to produce their genotoxic response. The aim of this study was to investigate if quinolone genotoxicity involves mammalian TOP2. Using the micronucleus assay, the genotoxicity of two quinolones ciprofloxacin and gemifloxacin was tested in three Nalm-6 cell lines containing varying amounts of TOP2. With ciprofloxacin only the Nalm-6TOP2A+/- cells showed genotoxicity, whereas for gemifloxacin only the Nalm-6 WT cells showed genotoxicity, suggesting that for gemifloxacin the removal of TOP2A or TOP2B lowers the genotoxicity of the quinolone. A selection of quinolones were tested using the Trapped in AgaRose DNA ImmunoStaining (TARDIS) assay to determine whether they stabilise the TOP2-DNA complexes in mammalian cells as known TOP2 poisons do. The analysis showed that after three hours incubation the level of complexes increased, indicating that the quinolones are able to stabilise TOP2-DNA complexes. Taken together the micronucleus and TARDIS assay data show that the quinolones are targeting mammalian TOP2 at high concentrations.

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior
Os bufodienolÃdeos sÃo esterÃides cardioativos de 24 carbonos, isolados originalmente de um extrato de pele de sapos da famÃlia Bufonidae utilizado na medicina chinesa. Os bufodienolÃdeos possuem grande variedade de atividades biolÃgicas, incluindo atividades antineoplÃsicas. Em relaÃÃo à atividade antitumoral, os bufodienolÃdeos tem demonstrado inibir o crescimento de vÃrias linhagens de cÃlulas cancerÃgenas humanas por induzir apoptose e parada do ciclo celular. O presente estudo avaliou o potencial citotÃxico e genetÃxico de seis bufodienolÃdeos em seis linhagens tumorais humanos, trÃs linhagens murinas normais e cÃlulas mononucleadas do sangue perifÃrico (CMSP) humano. Todos os seis bufodienolÃdeos foram citotÃxicos para todas as linhagens tumorais e CMSP com valores de IC50 variando entre 0,002 e 3,17 ÂM. Os bufodienolÃdeos testados nÃo apresentaram citotoxicidade para linhagens murinas normais. Desta forma, o composto hellebrigenina foi escolhido para se determinar o mecanismo de aÃÃo envolvido. Uma sequÃncia de experimentos in vitro foram realizados utilizando-se a linhagem leucÃmica HL-60. As cÃlulas foram tratadas em diferentes concentraÃÃes da amostra hellebrigenina (0,03, 0,06 e 0,12 ÂM) por 24 horas. A viabilidade das cÃlulas (nÃmero de cÃlulas viÃveis e integridade de membrana) HL-60 avaliada por citometria de fluxo, mostrou que o nÃmero de cÃlulas reduziu a partir da menor concentraÃÃo (0,03 ÂM) testada e a porcentagem de cÃlulas com membrana integra reduziu a partir da concentraÃÃo 0,06 ÂM. A anÃlise morfolÃgica por citometria de fluxo revelou aumento de cÃlulas com padrÃo apoptÃtico a partir da concentraÃÃo de 0,06 ÂM. Jà a anÃlise do conteÃdo nuclear, nos mostrou aumento de fragmentaÃÃo de DNA sub-G1 indicativo de apoptose e acÃmulo de cÃlulas na fase G2/M a partir das concentraÃÃes de 0,03 e 0,06 ÂM, respectivamente. Outros testes por citometria de fluxo revelaram que houve externalizaÃÃo da fosfatidilserina, despolarizaÃÃo mitocondrial, ativaÃÃo da caspase iniciadora 8 e consequente ativaÃÃo das caspases efetoras 3 e 7. Estes dados indicam um mecanismo citotÃxico por induÃÃo de mais de uma via apoptÃtica. Hellebrigenina nÃo foi capaz de causar danos ao DNA de HL-60 e de CMSP e nem o surgimento de aberraÃÃes cromossÃmicas em CMSP. Por meio dos estudos de docking molecular foi possÃvel predizer a ligaÃÃo entre hellebrigenina e topoisomeraseIIα humana, resultado compatÃvel com a possÃvel inibiÃÃo dessa enzima. De forma geral, os resultados apontam o potencial citotÃxico do bufodienolÃdeo hellebrigenina
Bufodienolides are cardioactive steroids of 24 carbons, originally isolated from a frogâs skin extract of the family Bufonidae used in Chinese medicine. Bufodienolides shows many biological activities, including anticancer activities. Related to antitumor activity, the bufodienolÃdeos has been shown to inhibit the growth of several human cancer cell lines by inducing apoptosis and cell cycle arrest. This study evaluated the potential cytotoxicity and genotoxicity of six bufodienolides, in six human tumor cell lines, three normal murine lineages and PBMC (peripheral blood mononuclear cells). All six bufodienolides were cytotoxic to all cell lines and tumor PBMC with IC50 values ranging from 0.002 to 3.17 ÂM. Bufodienolides showed no cytotoxicity for normal murine strains. Thus, the compound hellebrigenin was chosen to determine the action mechanism involved, a sequence of in vitro experiments were performed using HL-60 leukemia cell line. Cells were treated at different concentrations of hellebrigenin (0.03, 0.06 and 0.12 ÂM) for 24 hours. Cell viability (viable cell number and membrane integrity) HL-60 assessed by flow cytometry showed that the number of cells decreased from the lower concentration (0.03 ÂM) tested and the percentage of cells with reduced membrane integrity from 0.06 ÂM concentration. Morphological analysis by flow cytometry revealed increased apoptotic cells starting at concentrations of 0.06 ÂM. The analysis of nuclear content, showed an increase in DNA fragmentation indicative of sub-G1 apoptosis and accumulation of cells in G2 / M phase from the concentrations of 0.03 and 0.06 ÂM, respectively. Other tests by flow cytometry revealed that there was an externalization of phosphatidylserine, mitochondrial depolarization, activation of caspase 8 and initiating subsequent activation of effector caspases 3 and 7. These data indicate a cytotoxic mechanism induced by over an apoptotic pathway. Hellebrigenin was not able to cause DNA damage in HL-60 and PBMC nor the emergence of chromosomal aberrations in PBMC. Through the studies of molecular docking was possible to predict the connection between hellebrigenina and human topoisomeraseIIα, showing a result that is compatible with a possible inhibition of this enzyme. Overall, the results indicate the potential cytotoxicity of hellebrigenin

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Objetivos: Estudar a expressao imuno-histoquimica de topoisomerase IIƒ¿ e de caspase-3 ativada, marcadores de proliferacao e de apoptose, respectivamente, a deteccao de DNA HPV e a evolucao da lesao cervical em mulheres portadoras de lesao intra-epitelial escamosa de baixo grau (LBG). Metodos: Foram avaliadas 40 mulheres portadoras de LBG e 32 sem neoplasia cervical, diagnosticadas por exame cito-colpo-histopatologico, quanto a imunoexpressao de topoisomerase IIƒ¿ e de caspase-3 ativada e quanto a deteccao de DNA HPV por PCR consensual (GP5+/GP6+) em material de esfregaco cervico-vaginal. Os achados foram relacionados as variaveis clinicas das pacientes e a evolucao clinica das lesoes cervicais em 12 meses. As pacientes assinaram termo de consentimento livre e esclarecido. Resultados: A media percentual de celulas imunomarcadas por topoisomerase foi de 11,71% e 4,13%, no grupo com LBG e controle, respectivamente, com diferenca estatisticamente significante. Observou-se que houve expressao de caspase-3 em 17 (42,5%) e em 5 (15,63%) pacientes com e sem LBG, respectivamente, com diferenca estatisticamente significante. Foi detectado HPV DNA em 65% das pacientes com LBG e em 59,4% das pacientes sem lesao cervical, sem relacao com a expressao de topoisomerase IIƒ¿ ou caspase-3. Na presenca de DNA-HPV, a expressao de topoisomerase IIƒ¿ no grupo com LBG foi significativamente maior do que em fragmentos sem lesao. Nao foi observada diferenca quanto a evolucao da lesao cervical em 12 meses de acordo com a imunoexpressao de topoisomerase IIƒ¿. Com relacao a caspase-3 ativada, a maioria das pacientes com imuno-histoquimica negativa teve regressao da lesao cervical. Conclusoes: A imunoexpressao de topoisomerase IIƒ¿ e de caspase-3 ativada podem ser considerados marcadores de proliferacao e de apoptose em lesao cervical de baixo grau, sem relacao com a presenca de DNA-HPV.
Purpose: To evaluate the correlation between the expression of topoisomerase II alpha, active caspase-3 and infection with human papillomavirus in low-grade cervical intraepithelial lesion and in the normal cervix, and whether they might influence susceptibility to, or evolution of, cervical lesion. Patients and methods: Forty cervical biopsies patients with low-grade cervical intraepithelial lesion and thirty-two with normal cervix were stained by immunohistochemistry for topoisomerase IIá and active caspase-3 and were investigated for the presence of HPV on exfoliated cells by general primer GP5+/6+ PCR amplification of DNA. These findings were correlated with clinicopathological features of the patients including their clinical outcome after twelve months. Subjects provided written informed consent. Results: Low-grade CIN patients as a group had a significantly higher expression of topoisomerase II alpha compared to controls, without correlation to disease outcome at 12 months. Caspase-3 was expressed in 42.5% of CIN patients and in 15.63% without disease, and most of women without caspase-3 receded cervical lesion. HPV DNA testing was positive in 65% of the patients with cervical lesion, and in 59.4% of the control group and was not associated to the expression of topoisomerase IIá or active caspase-3. In the presence of a positive HPV DNA testing, women with cervical lesion had a significantly higher expression of topoisomerase II alpha compared to controls. Conclusion: Topoisomerase II alpha and active caspase-3 might be useful diagnostic and prognostic markers in low-grade cervical lesions, delaying a better follow-up.
CNPq: 134106/2005-9
TEDE
BV UNIFESP: Teses e dissertações

INTRODUÇÃO: A endometriose, uma doença benigna, tem características invasivas com potencial proliferativo. O desenvolvimento das lesões pode ocorrer em decorrência de crescimento celular glandular e/ou estromal ou de alterações na cinética celular. Cinética celular refere-se ao equilíbrio entre a morte celular, ou apoptose, e a proliferação celular, que pode ser avaliada pela expressão de fatores de crescimento como, por exemplo, a topoisomerase 2-alfa (TOP2A). Também influenciam a cinética celular oncoproteínas como p53 e c-erB2, conhecidas por interferir na apoptose, podendo resultar em oncogênese. OBJETIVOS: O objetivo principal deste estudo foi comparar a cinética celular da endometriose infiltrativa de retosigmoide com a do endométrio eutópico de pacientes sem endometriose. Para tanto, foi avaliada a expressão de apoptose e de TOP2A bem como das oncoproteínas p53 e c-erB2. MÉTODOS: Foram obtidas amostras de lesões de endometriose envolvendo o reto-sigmoide de 60 mulheres com a doença e amostras de endométrio eutópico de 20 mulheres sem endometriose. A expressão de TOP2A e das proteínas p53 e c-erB2 foram quantificadas por técnica imuno-histoquímica. Método TUNEL foi utilizado para analisar os padrões de apoptose, que resultaram em índice de apoptose (IA). Índice de proliferação celular (IP) foi determinado a partir do nível de expressão de TOP2A. Índice de renovação celular (IRC) foi calculado pela razão entre IP e IA. As análises imuno-histoquímicas foram realizadas tanto no tecido endometrial como um todo, quanto nos componentes estromal e glandular separadamente. Coeficiente de Correlação de Spearman foi aplicado para identificar eventuais correlações entre variáveis clínicas, morfológicas (tamanho, quantidade e nível de invasão das lesões) e experimentais. RESULTADOS: Na análise da amostra do tecido como um todo, não foram evidenciadas diferenças entre os grupos experimental e controle em relação ao IA (p = 0,389). Por outro lado, o IP foi significativamente maior nas amostras-controle (p < 0,001). Na avaliação em que se sepaxii raram as células estromais dos componentes glandulares, tanto o IP quanto o IRC foram significativamente maiores no grupo-controle em comparação com o grupo experimental (IP estromal: p = 0,006; IP glandular: p = 0,001; IRC estromal: p =0,032; IRC glandular: p = 0,007). Nas pacientes com endometriose, foi encontrada correlação entre IP e IRC glandular e o número de lesões (p = 0,003). Também foi observada correlação entre o IRC glandular e o tamanho das lesões (p = 0,006). Não houve diferença entre os grupos no que se refere à expressão de p53 e cerB2. CONCLUSÕES: A cinética celular se mostrou alterada em pacientes com endometriose do reto-sigmoide, conforme demonstrado pela redução nos níveis e na frequência de TOP2A, e pelos IP e IRC mais baixos; entretanto, apoptose e as expressões de p53 e c-erB2 se mostraram inalteradas
BACKGROUND: Endometriosis, a benign disease, has invasive features with its proliferative potential. Development of lesions may occur due to stromal and/or glandular cell growth and to alterations in cellular kinetics. Cellular kinetics involves a balance between the regulation of cell death, or apoptosis, and cell growth, that can be evaluated by the expression of growth factors, such as topoisomerase 2- alpha (TOP2A). Oncoproteins, such as p53 and c-erB2, known to affect apoptosis resulting in oncogenesis, also influence cellular kinetics. OBJECTIVES: The main objective of this study was to compare the cellular kinetics in deep endometriosis involving the recto-sigmoid to eutopic endometrium from patients without endometriosis. Apoptosis and TOP2A expression were primarily evaluated, as well as p53 and c-erB2 expression. METHODS: Study samples were obtained from endometriosis lesions involving the recto-sigmoid in 60 women, and control samples were obtained from eutopic endometrium from 20 women without endometriosis. The expression of TOP-2A, p53 and c-erB2 proteins were quantified using immuno-histochemistry. TUNEL method was used in the analysis of apoptosis patterns, and the apoptosis index (AI) was derived. The proliferation index (PI) was derived from the level of expression of TOP-2A. Cellular renew index (CRI) was calculated from the ratio of the PI and AI. Immunohistochemical analyses were performed in two ways: on the tissue collectively, and on the stromal and glandular components separately. Spearmans correlation coefficient was used to identify the correlation between clinical, morphological (size, number and level of invasion of lesions) and the study variables. RESULTS: When looked at collectively, there was no difference in the AI between study and control groups (p = 0.389). PI, however, was noted to be significantly higher in the control samples (p < 0.001). When evaluating the stromal cells separately from the glandular components, the PI and CRI were both significantly xiv higher in the control group compared to the study group (Study stromal PI vs control stromal PI; p = 0.006; Study glandular PI vs study glandular PI; p = 0.001; Study stromal CRI vs control stromal CRI; p = 0.032; study glandular CRI vs control glandular CRI; p = 0.007). In patients with endometriosis, a correlation was found between glandular PI, CRI and number of lesions (p = 0.003). The same result was observed in the analysis of stromal CRI and lesion size (p = 0.006). There was no difference in expression of p53 and c-erB2 between groups. CONCLUSIONS: Cellular kinetics is altered in endometriosis of the recto-sigmoid, as shown by the decrease in the levels and frequency of TOP2A expression, and lower PI and CRI; however, apoptosis and p53 and c-erB2 expression were unaffected

Interactions between the retinoic acid receptor alpha (RARalpha) and coregulators play a key role in coordinating gene transcription and myeloid differentiation. In acute promyelocytic leukemia (APL), RARalpha is fused with the promyelocytic leukemia (PML) gene, resulting in the expression of the fusion protein PML/RARalpha. Here, I report that topoisomerase II beta (topoIIbeta) associates with and negatively modulates PML/RARalpha and RARalpha transcriptional activity, and increased levels and association of topoIIbeta cause resistance to retinoic acid (RA) in APL cell lines. Knock down of topoIIbeta was able to overcome resistance by permitting RA-induced differentiation and increased RA-gene expression. Overexpression of topoIIbeta, in clones from an RA-sensitive cell line, conferred resistance by a reduction in RA-induced expression of target genes and differentiation. Chromatin immunoprecipitation assays indicate that topoIIbeta is bound to an RA-response element, and inhibition of topoIIbeta causes hyper-acetylation of histone 3 at lysine 9 and activation of transcription. These results identify a novel mechanism of resistance in APL and provide further insights to the role of topoIIbeta in gene regulation and differentiation.
Studies to determine the mechanism by which topoIIbeta protein is regulated found that levels of protein kinase C delta (PKCdelta) correlated with topoIIbeta protein expression. Moreover, activation of PKCdelta, by RA or PMA, led to an increase of topoIIbeta protein levels. Most notably, in NB4-MR2 cells, we observed increased phosphorylation levels of threonine 505 on PKCdelta, a marker of activation. Inhibition of PKCdelta was able to overcome the topoIIbeta repressive effects on RA-target genes. In addition, the combination of RA and PKCdelta inhibition led to increased expression of the granulocytic marker, CD11c, in NB4 and NB4-MR2 cells. These results suggest that PKCdelta regulates topoIIbeta expression, and a constitutively active PKCdelta in the NB4-MR2 cell line leads to overexpression of topoIIbeta.
In conclusion, these studies demonstrate that topoIIbeta associates with RARalpha, binds to RAREs and plays a critical role in RA dependent transcriptional regulation and granulocytic differentiation. In addition, I show that topoIIbeta overexpression leads to RA resistance and provide evidence that topoIIbeta protein levels are regulated via a mechanism involving the PKCdelta pathway. This work has contributed to an enhanced understanding of the role of topoIIbeta in gene regulation and brings novel perspectives in the treatment of RA-resistance in APL.

DNA topoisomerases are vital enzymes for major cellular processes like replication, transcription, and chromosome segregation. They play an essential role in solving DNA topological problems by catalysing the passage of DNA strands through each other via introducing transient single or double strand breaks. Type IIA DNA topoisomerases members introduce double strand breaks via an ATP-dependent strand passage reaction. This study aimed to investigate the roles of topo Ila and topo Iip in zebrafish development.

碩士
國立中興大學
生物化學研究所
91
Type II DNA topoisomerases are essential cellular enzymes which alter the topological state of DNA. They are involved in all aspects of DNA metabolism including DNA replication, transcription, recombination, and chromosome segregation. All type II topoisomerases use an ATP-coupled DNA transport reaction in which the enzyme cleaves and generates a "gate" on one DNA duplex (termed G-segment), transports a second duplex (termed T-segment) through the break, and subsequently religates the cleaved DNA. Many antitumor and antibacterial drugs inhibit type II DNA topoisomerase by trapping covalent enzyme-DNA cleavage complexes. Formation of cleavage complexes is important for the cytotoxicity of these drugs. Although type II enzymes interact extensively with DNA, the protein-DNA interaction is yet to be structurally characterized. This experiment is aimed to at determing the following crystal structures: 1) the crystal structure of the DNA cleavage/ rejoin domain of bacteriophage T2 topoisomerase (gene 52 protein), 2) the structures of the protein-DNA complex(es), 3) structure(s) of protein-DNA-drug ternary complex(es). Previous studies show that the gene 52 protein has a disorder region in the N- terminus that may interfere with crystallization, therefore I use a truncation mutant of gene 52 protein, (termed Tr-11, in which the 11 N-terminal residues were removed) for structural analysis. Large quantity of Tr-11 protein can be obtained following ammonium sulfate precipitation, hydroxyapatite chromatography, and gel filtration chromatography, and crystals of Tr-11 protein were found in the condition consisted of 15% PEG 4K、0.1 M sodium citrate pH 5.6、0.2 M ammonium acetate. However, only low resolution diffraction was observed from these crystals. Finally I used a internal deletion mutant of gene 52 protein (termed ΔT2-52-5g, in which residues 342 to 418 were replaced by a glycine-linker) for crystallization and crystals were found in 18% PEG 8K、0.1M sodium cacodylate pH 6.5、0.2M calcium acetate .In addition, crystallization of ΔT2-52-5g/DNA complex has also been initated.

碩士
國立臺灣大學
生物化學暨分子生物學研究所
97
The intertwined structure of duplex DNA is known to cause topological problems during DNA transactions, in which processive strand unwinding generates the under- and over-winding on the flanking duplex regions. If not removed, the accumulation of superhelical strains will halt DNA duplication and gene expression. In addition, newly replicated daughter chromosomes are interlinked and must be segregated prior to cell division. In bacteria, two closely related yet functionally distinct type IIA topoisomerases (topos), DNA gyrase and topo IV, are responsible for resolving these topological problems. With the unique (-) supercoiling activity, gyrase removes the (+) supercoils in front of the replication forks and maintains bacterial genomes in a slightly underwound state, promoting the initiation of transcription and replication. In contrast, topo IV is specialized for decatenation of tangled daughter chromosomes. For most bacteria, these two enzymes are both essential and work in concert to maintain the superhelical homeostasis. However, a few eubacteria possess only one type II topo. It remains controversial whether this lone type II topo functions mainly as a gyrase or a topo IV, or if it possesses both the (-) supercoiling and decatenation activities, to sustain cell viability. Here we characterized the lone type II topo encoded by the genome of Aquifex aeolicus, a hyperthermophilic eubacterium. This enzyme is currently annotated as a gyrase, composed of the GyrB and GyrA subunits. However, sequence analysis reveals that the C-terminal domain of A. aeolicus GyrA (aeGyrA-CTD), a domain known to confer the (-) supercoiling activity of gyrase, is very different from other GyrA-CTD. Specifically, the aeGyrA-CTD is significantly shorter in length and lacks a characteristic GyrA box (QRRGGKG) found in all gyrases. These differences may contribute to its unique activity as the sole type II topo. The A. aeolicus topo II was purified to homogeneity, whose optimal activity was observed at around 85℃, consistent with the extremely high growing temperature of this bacterium. At 85℃ A. aeolicus topo II was found to introduce (-) supercoils into relaxed DNA molecules, indicating that it may function as a gyrase. Surprisingly, while other gyrases require ATP to drive this reaction, A. aeolicus topo II is not strictly ATP-dependent. Furthermore, when the (-) supercoiled DNA was incubated with A. aeolicus topo II, it becomes more relaxed even in the presence of ATP. These properties are distinct from those of E. coli gyrase, whose (-) supercoiling activity requires ATP and it does not exhibit relaxation activity in the presence of ATP. In addition, A. aeolicus topo II efficiently resolves interlinked kDNA network, suggesting that it may act as a topo IV-like decatenase in vivo. Therefore, A. aeolicus topo II is unique in that, depending on substrates, either (-) supercoiling or relaxation activity can be observed, with both activities being accelerated by ATP hydrolysis. Moreover, removal of aeGyrA-CTD merely reduces the reaction rate but the catalytic pattern of A. aeolicus topo II on different substrates was not affected, indicating that this domain does not play a dominant role in mediating the holoenzyme activity. The unique ATP-independent supercoiling activity at high temperature can be explained by relaxation of (+) supercoils. Due to the emergence of compensatory (+) supercoils on relaxed closed circular DNA associated with DNA unwinding at high temperature, A. aeolicus topo II releases the free energy stored as (+) supercoils to achieve DNA relaxation. Therefore, it appears that A. aeolicus topo II possesses merely relaxation and no (-) supercoiling activity, and the relaxation process is further facilitated by ATP hydrolysis, where the nucleotide binding-induced structural changes leads to more efficient capture of a second DNA segment for strand passage. The biased activity toward DNA relaxation of A. aeolicus topo II seems reasonable with the concomitant presence of the hyperthermophilic-specific reverse gyrase in vivo. Reverse gyrase actively generates (+) supercoils to overcome DNA denaturation, wheras A. aeolicus topo II functions as a decatenase to support chromosome segregation. In addition, this enzyme also relaxes excessive superhelical strains to maintain DNA superhelical homeostasis. By harboring efficient relaxation and decatenation activities, A. aeolicus topo II is functionally more related to bacterial topo IV. Being one of the earliest diverging eubacteria, our result implicates that the relaxation/decatenation activity evolved earlier in the prototype of topo II, and (-) supercoiling activity may not be required for the growth of ancient bacteria. Further studies on other type II topos from a wide range of bacteria will provide more information regarding how the topoisomerase activity can be fine-tuned to meet specific physiological requirements.