Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Borrelia burgdorferi, the agent of Lyme disease, has recently joined a growing number of micro-organisms for which the entire genomic sequence is known. Despite this wealth of information, little is known about the contribution of specific spirochetal components to the pathogenesis of Lyme disease or their function in the normal life cycle of the organism. This discrepancy is due in part to the lack of a well-developed genetic system in B. burgdorferi, which in turn can be attributed to its relatively recent isolation and the dissimilarity of Borrelia from other genetically tractable bacteria. We are interested in several plasmid-encoded gene products in B. burgdorferi that may play a role in sensing and adaptation to the different environments the spirochete encounters as it completes an infectious cycle between the tick vector and the mammalian host. We are developing genetic tools with which to test the roles of specific B. burgdorferi gene products in the transmission cycle in an animal model of Lyme disease. We have demonstrated targeted gene inactivation by allelic exchange, using the gyrBr gene encoding coumermycin-resistant topoisomerase as a selectable marker. Spirochetes are transformed by electroporation and coumermycin-resistant colonies are screened by PCR for allelic exchange at the targeted locus. We have successfully inactivated several genes of interest in the type strain B31. We are investigating the utility of additional antibiotic resistance genes as selectable markers in B. burgdorferi. Targeted gene inactivation is a powerful tool with which to investigate the role of particular proteins in the basic biology and virulence of a pathogenic microorganism. We have made significant advances in our ability to genetically manipulate B. burgdorferi in order to address these issues. However, the available methods are incomplete and far from routine. We are currently improving existing methods as well as developing additional genetic tools with which to augment genetic studies in B. burgdorferi.
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PMID:Genetic studies in Borrelia burgdorferi. 1004 65

Holliday junction resolvases (HJRs) are key enzymes of DNA recombination. A detailed computer analysis of the structural and evolutionary relationships of HJRs and related nucleases suggests that the HJR function has evolved independently from at least four distinct structural folds, namely RNase H, endonuclease, endonuclease VII-colicin E and RusA. The endonuclease fold, whose structural prototypes are the phage lambda exonuclease, the very short patch repair nuclease (Vsr) and type II restriction enzymes, is shown to encompass by far a greater diversity of nucleases than previously suspected. This fold unifies archaeal HJRs, repair nucleases such as RecB and Vsr, restriction enzymes and a variety of predicted nucleases whose specific activities remain to be determined. Within the RNase H fold a new family of predicted HJRs, which is nearly ubiquitous in bacteria, was discovered, in addition to the previously characterized RuvC family. The proteins of this family, typified by Escherichia coli YqgF, are likely to function as an alternative to RuvC in most bacteria, but could be the principal HJRs in low-GC Gram-positive bacteria and AQUIFEX: Endonuclease VII of phage T4 is shown to serve as a structural template for many nucleases, including MCR:A and other type II restriction enzymes. Together with colicin E7, endonuclease VII defines a distinct metal-dependent nuclease fold. As a result of this analysis, the principal HJRs are now known or confidently predicted for all bacteria and archaea whose genomes have been completely sequenced, with many species encoding multiple potential HJRs. Horizontal gene transfer, lineage-specific gene loss and gene family expansion, and non-orthologous gene displacement seem to have been major forces in the evolution of HJRs and related nucleases. A remarkable case of displacement is seen in the Lyme disease spirochete Borrelia burgdorferi, which does not possess any of the typical HJRs, but instead encodes, in its chromosome and each of the linear plasmids, members of the lambda exonuclease family predicted to function as HJRs. The diversity of HJRs and related nucleases in bacteria and archaea contrasts with their near absence in eukaryotes. The few detected eukaryotic representatives of the endonuclease fold and the RNase H fold have probably been acquired from bacteria via horizontal gene transfer. The identity of the principal HJR(s) involved in recombination in eukaryotes remains uncertain; this function could be performed by topoisomerase IB or by a novel, so far undetected, class of enzymes. Likely HJRs and related nucleases were identified in the genomes of numerous bacterial and eukaryotic DNA viruses. Gene flow between viral and cellular genomes has probably played a major role in the evolution of this class of enzymes. This analysis resulted in the prediction of numerous previously unnoticed nucleases, some of which are likely to be new restriction enzymes.
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PMID:SURVEY AND SUMMARY: holliday junction resolvases and related nucleases: identification of new families, phyletic distribution and evolutionary trajectories. 1098 59

We have isolated in vitro fluoroquinolone-resistant mutants of the Lyme disease agent, Borrelia burgdorferi. Mutations in parC, which encodes a subunit of topoisomerase IV, were associated with loss of susceptibility to sparfloxacin, moxifloxacin, and Bay-Y3118, but not ciprofloxacin. This is the first description of fluoroquinolone resistance in the spirochete phylum.
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PMID:parC mutations in fluoroquinolone-resistant Borrelia burgdorferi. 1618 20