title: Complete mitochondrial genome sequence of Urechis caupo, a representative of the phylum Echiura.
abstract: BACKGROUND
  Mitochondria contain small genomes that are physically separate from those of nuclei. Their comparison serves as a model system for understanding the processes of genome evolution. Although hundreds of these genome sequences have been reported, the taxonomic sampling is highly biased toward vertebrates and arthropods, with many whole phyla remaining unstudied. This is the first description of a complete mitochondrial genome sequence of a representative of the phylum Echiura, that of the fat innkeeper worm, Urechis caupo.
  
  
  RESULTS
  This mtDNA is 15,113 nts in length and 62% A+T. It contains the 37 genes that are typical for animal mtDNAs in an arrangement somewhat similar to that of annelid worms. All genes are encoded by the same DNA strand which is rich in A and C relative to the opposite strand. Codons ending with the dinucleotide GG are more frequent than would be expected from apparent mutational biases. The largest non-coding region is only 282 nts long, is 71% A+T, and has potential for secondary structures.
  
  
  CONCLUSIONS
  Urechis caupo mtDNA shares many features with those of the few studied annelids, including the common usage of ATG start codons, unusual among animal mtDNAs, as well as gene arrangements, tRNA structures, and codon usage biases.
authors.affiliation: Evolutionary Genomics Department, DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, 2800 Mitchell Drive, Walnut Creek, CA, USA. jlboore@lbl.gov.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Boore
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D000845:Annelida / Q000235:genetics*; D001482:Base Composition / Q000235:genetics; D001483:Base Sequence / Q000235:genetics; D003062:Codon / Q000235:genetics; D018388:Codon, Terminator / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics*; D005796:Genes / Q000235:genetics; D016678:Genome; D008928:Mitochondria / Q000235:genetics*; D008969:Molecular Sequence Data; D012335:RNA, Ribosomal / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics; D024363:Transcription Initiation Site
chemical_list: D003062:Codon; D018388:Codon, Terminator; D021901:DNA, Intergenic; D004272:DNA, Mitochondrial; D012335:RNA, Ribosomal; D012343:RNA, Transfer