title: Mitochondrial DNA ligases of Trypanosoma brucei.
abstract: The mitochondrial DNA of Trypanosoma brucei, termed kinetoplast DNA or kDNA, consists of thousands of minicircles and a small number of maxicircles catenated into a single network organized as a nucleoprotein disk at the base of the flagellum. Minicircles are replicated free of the network but still contain nicks and gaps after rejoining to the network. Covalent closure of remaining discontinuities in newly replicated minicircles after their rejoining to the network is delayed until all minicircles have been replicated. The DNA ligase involved in this terminal step in minicircle replication has not been identified. A search of kinetoplastid genome databases has identified two putative DNA ligase genes in tandem. These genes (LIG k alpha and LIG k beta) are highly diverged from mitochondrial and nuclear DNA ligase genes of higher eukaryotes. Expression of epitope-tagged versions of these genes shows that both LIG k alpha and LIG k beta are mitochondrial DNA ligases. Epitope-tagged LIG k alpha localizes throughout the kDNA, whereas LIG k beta shows an antipodal localization close to, but not overlapping, that of topoisomerase II, suggesting that these proteins may be contained in distinct structures or protein complexes. Knockdown of the LIG k alpha mRNA by RNA interference led to a cessation of the release of minicircles from the network and resulted in a reduction in size of the kDNA networks and rapid loss of the kDNA from the cell. Closely related pairs of mitochondrial DNA ligase genes were also identified in Leishmania major and Crithidia fasciculata.
authors.affiliation: Molecular Biology Institute and Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, California 90095-1570, USA.
authors.forename: Nick
authors.initials: N
authors.lastname: Downey
authors.forename: Jane C
authors.initials: JC
authors.lastname: Hines
authors.forename: Krishna M
authors.initials: KM
authors.lastname: Sinha
authors.forename: Dan S
authors.initials: DS
authors.lastname: Ray
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D018105:DNA, Kinetoplast / Q000235:genetics / Q000378:metabolism*; D004272:DNA, Mitochondrial / Q000235:genetics*; D016054:DNA, Protozoan / Q000235:genetics*; D019992:Databases as Topic; D016678:Genome; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D034622:RNA Interference; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014346:Trypanosoma brucei brucei / Q000201:enzymology / Q000235:genetics* / Q000648:ultrastructure
chemical_list: D018105:DNA, Kinetoplast; D004272:DNA, Mitochondrial; D016054:DNA, Protozoan; D012333:RNA, Messenger; D004250:DNA Topoisomerases, Type II; D011088:DNA Ligases