Disease relevance of Top1

• Using a single-molecule micromanipulation setup, we follow the real-time decatenation of two mechanically braided DNA molecules by Drosophila melanogaster topoisomerase (Topo) II and Escherichia coli Topo IV [1].
• Similar to the DNA knotting reaction by bacteriophage T4-induced topoisomerase (Liu, L [2].
• Topoisomerase II (top2) has been implicated in the initial steps of chromosomal translocations leading to leukemias and lymphomas, since it can generate DNA cleavage [3].
• In an animal model of cryptococcal meningitis, topoisomerase I regulation was not critically important to established infection, but may impact on the initial stress response to infection [4].
• In contrast, alterations in topoisomerase I levels had no effect on the toxicity of a novel class of antifungal agents, the dicationic aromatic compounds (DACs), indicating that topoisomerase I is not the target of DACs [4].

High impact information on Top1

• The in vivo distribution of topoisomerase I on specific DNA sequences is determined at high resolution in Drosophila cells using a photo-crosslinking method [5].
• Like RNA polymerase II, topoisomerase I is recruited to heat-shock genes during the heat-shock response [5].
• The Drosophila ATP-dependent topoisomerase appears to be closely related to E. coli DNA gyrase in that both use a similar mechanism to change the topology of DNA, both require ATP and both are inhibited by the antibiotic novobiocin [6].
• We have identified a factor, Drosophila Topoisomerase I-interacting RS protein (dTopors) that interacts with the insulator protein complex and is required for gypsy insulator function [7].
• Although Topo II relaxes left-handed (L) and right-handed (R-) braids similarly at a rate of approximately 2.9 s-1, Topo IV has a marked preference for L-braids, which it relaxes completely and processively at a rate of approximately 2.4 s-1 [1].

Biological context of Top1

• This enzyme partially relaxes a hypernegatively supercoiled plasmid substrate consistent with other purified topo IIIs [8].
• In this study, we cloned Drosophila melanogaster topoisomerase (topo) IIIalpha from an embryonic cDNA library and expressed and purified the protein to >95% homogeneity [8].
• Expression patterns for topoisomerase I and topoisomerase II during the embryogenesis of Drosophila melanogaster were compared with patterns of DNA replication and expression of the histone genes [9].
• A high level of top1 mRNA transcript was present without differential tissue distribution throughout embryogenesis [9].
• Loss of the ring X chromosome (rX), was significantly enhanced by CPT, and this topoisomerase blocker also produced intra-chromosomal recombination (XY males) [10].

Anatomical context of Top1

• Protein kinase C phosphorylates topoisomerase II: topoisomerase activation and its possible role in phorbol ester-induced differentiation of HL-60 cells [11].
• A correlation between reduced expression of Gadd45 and increased resistance to topoisomerase I and topoisomerase II inhibitors in a variety of human cell lines was also found [12].
• Interaction in vitro of type III intermediate filament proteins with supercoiled plasmid DNA and modulation of eukaryotic DNA topoisomerase I and II activities [13].
• RNA blot hybridization showed that oocytes contain an abundant store of somatic topoisomerase I mRNA that is not efficiently polyadenylated in oocytes [14].
• In vitro transcription was reconstituted with HeLa cell transcription factors and RNA polymerase II, which were essentially free from DNA topoisomerase activities [15].

Associations of Top1 with chemical compounds

• Drosophila topoisomerase IIIbeta forms a covalent linkage to 5' DNA phosphoryl groups, and the DNA cleavage reaction prefers single-stranded substrate over double-stranded, suggesting an affinity of this enzyme for DNA with non-double-helical structure [16].
• The top1 coding region contains a new class of opa repeats, encoding clusters of serine residues instead of glutamine repeats usually seen in Drosophila genes of the neurogenic loci [17].
• The kinase and topoisomerase activities are not separated when the enzyme is subjected to analytical chromatography (phosphocellulose, single-strand DNA agarose, and Sephacryl S-300) and analytical glycerol gradient sedimentation [18].
• Phosphoamino acid analysis identified phosphoserine and phosphothreonine in polypeptides modified by the topoisomerase-associated protein kinase [18].
• Calmodulin-dependent protein kinase II, but not cyclic AMP-dependent protein kinase, was also able to phosphorylate the topoisomerase [11].

Physical interactions of Top1

• Topoisomerase I also interacted with the DNA throughout the transcriptionally active hsp83 gene, including an intron, in both heat-shocked and non-heat-shocked cells [19].

Other interactions of Top1

• The top3 cDNA encodes an 875-amino acid protein, which is nearly 60% identical to mammalian topoisomerase IIIbeta enzymes [16].
• These studies suggest that the topo III enzyme behaves as a structure-specific endonuclease in vivo, providing a reversible DNA cleavage activity that is specific for unpaired regions in the DNA [20].
• The ATPase activity of the topoisomerase was stimulated 17-fold by the presence of negatively supercoiled DNA and approximately 4 molecules of ATP were hydrolyzed/supercoil removed [21].
• A model for achiasmatic pairing in Drosophila males based upon the combined action of topoisomerase I and a strand transferase is proposed [22].
• The presence of a putative site for topoisomerase I at the 5' end of the 18S rRNA gene would allow for the exchange between X and Y chromosomes of some 240 subrepeats, the promoter, and the ETS region, leaving the rest of the rDNA unit to evolve along separate chromosomal lineages [23].

Analytical, diagnostic and therapeutic context of Top1

• Southern blot analysis of yeast and Drosophila DNA using human alpha and beta specific probes detected a single topo II homologue in these lower eukaryotes [24].
• Microinjection into oocytes of in vitro transcribed mRNA prepared from a Myc-tagged construct of the somatic topoisomerase I sequence is translated to yield a 110 kDa product [14].
• Part of the topoisomerase I (TopoI)-encoding gene from Plasmodium falciparum (Pf) was isolated by PCR from cDNA using oligodeoxyribonucleotides modelled on the highly conserved regions of sequence from other species [25].
• Topoisomerase II-catalyzed ATP hydrolysis as monitored by thin-layer chromatography [26].
• Immunofluorescence staining of the polytene chromosomes of Drosophila shows high levels of topoisomerase I associated with transcriptionally active regions [27].

References