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DNA Topoisomerases, Type II definition: DNA TOPOISOMERASES that catalyze ATP-dependent breakage of both strands of DNA, passage of the unbroken strands through the breaks, and rejoining of the broken strands. These enzymes bring about relaxation of the supercoiled DNA and resolution of a knotted circular DNA duplex.
Topoisomerase II definition: Topoisomerase II catalyzes relaxation of supercoiled DNA molecules, catenation, decatenation, knotting, and unknotting of circular DNA. The topoisomerase II reaction appears to involve crossing-over of two DNA segments. Human cells contain two topoisomerase II isozymes: alpha and beta from distinct genes. DNA topoisomerase II alpha is associated with the Pol II holoenzyme and is required for chromatin-dependent co-activation. Transcription results in superhelical tension; topoisomerase II relaxation activity is essential for productive RNA synthesis on nucleosomal DNA. (from OMIM 126430 and NCI)
Topoisomerase II Alpha definition: Encoded by human TOP2A Gene (TOPII Family), alternative homodimeric nuclear DNA Topoisomerase II, Alpha isoforms 1 (1531-aa, 174.4-kD), 2 (1557-aa), 3 (1567-aa), and 4 (1612-aa) control DNA topology. TOP2A catalyzes transient ATP-dependent double-strand breakage/relaxation and rejoining of negative/positive supercoiled DNA during transcription, replication, chromosome condensation, and chromatid separation. TOPII reactions likely involve crossing-over. TOP2A is associated with Pol II holoenzyme. Inhibited by intercalating amsacrine, TOP2A is a target for several anticancer agents. Mutations are linked with drug resistance and perhaps ataxia-telangiectasia. (from LocusLink, Swiss-Prot, OMIM, and NCI)
Topoisomerase II Alpha definition: Involved in chromosome condensation and segregation, topoisomerase II alpha is a homodimer that controls DNA topology by transient ATP-dependent double-strand breakage and rejoining. Topoisomerase II alpha is also associated with the Pol II holoenzyme and required for chromatin-dependent co-activation and productive RNA synthesis. (from OMIM 126430 and NCI)
topoisomerase II alpha definition: This gene plays a role in DNA replication, chromosome recombination and the regulation of the DNA topology during transcription. Check for "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=464377&idtype=1" active clinical trials or "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=464377&idtype=1&closed=1" closed clinical trials using this agent. ("http://nciterms.nci.nih.gov:80/NCIBrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&code=C26592" NCI Thesaurus)
TOP2A Gene definition: This gene plays a role in DNA replication, chromosome recombination and the regulation of DNA topology during transcription.
Topoisomerase II Beta definition: Encoded by human TOP2B Gene (TOPII Family), alternative homodimeric nuclear DNA Topoisomerase II, Beta isoforms: 2 (1626-aa, 183-kD) and 1 (1621-aa) control DNA topology. TOP2B catalyzes transient ATP-dependent double-strand breakage/relaxation and rejoining of negative/positive supercoiled DNA during transcription, replication, chromosome condensation, and chromatid separation. With 72% similarity in TOP2, TOP2A/B N-terminal ATPase and central breakage/reunion domains are conserved; the C-terminal domains differ markedly. The TOP2B C-terminus contains potential phosphorylation sites. TOP2B is a target for several anticancer agents. Mutations are linked with drug resistance and perhaps ataxia-telangiectasia. (from LocusLink, Swiss-Prot, OMIM, and NCI)
Topoisomerase II Beta definition: Both topo II alpha and beta isoforms exhibit ATP-dependent strand passage activity, but they differ in several key aspects. The beta isoform relaxes DNA in a more progressive manner than the alpha isoform and also exhibits a higher optimal KCl requirement. The beta isoform has a molecular weight of 180 KD, and is immunologically distinct as well as exhibits different SV8 proteolytic cleavage pattern from alpha isoform.
 
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