title: Thirteen-exon-motif signature for vertebrate nuclear and mitochondrial type IB topoisomerases.
abstract: DNA topoisomerases contribute to various cellular activities that involve DNA. We previously identified a human nuclear gene that encodes a mitochondrial DNA topoisomerase. Here we show that genes for mitochondrial DNA topoisomerases (type IB) exist only in vertebrates. A 13-exon topoisomerase motif was identified as a characteristic of genes for both nuclear and mitochondrial type IB topoisomerases. The presence of this signature motif is thus an indicator of the coexistence of nuclear and mitochondrial type IB DNA topoisomerases. We hypothesize that the prototype topoisomerase IB with the 13-exon structure formed first, and then duplicated. One topoisomerase specialized for nuclear DNA and the other for mitochondrial DNA.
authors.affiliation: Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, NIH, DHHS, Bethesda, MD, USA.
authors.forename: Hongliang
authors.initials: H
authors.lastname: Zhang
authors.forename: Ling-Hua
authors.initials: LH
authors.lastname: Meng
authors.forename: Drazen B
authors.initials: DB
authors.lastname: Zimonjic
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Popescu
authors.forename: Yves
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology*; D016000:Cluster Analysis; D017124:Conserved Sequence / Q000235:genetics; D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics*; D020440:Gene Duplication; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D014714:Vertebrates / Q000235:genetics
chemical_list: D004264:DNA Topoisomerases, Type I