title: The non-LTR retrotransposons in Ciona intestinalis: new insights into the evolution of chordate genomes.
abstract: BACKGROUND
  Non-long terminal repeat (non-LTR) retrotransposons have contributed to shaping the structure and function of genomes. In silico and experimental approaches have been used to identify the non-LTR elements of the urochordate Ciona intestinalis. Knowledge of the types and abundance of non-LTR elements in urochordates is a key step in understanding their contribution to the structure and function of vertebrate genomes.
  
  
  RESULTS
  Consensus elements phylogenetically related to the I, LINE1, LINE2, LOA and R2 elements of the 14 eukaryotic non-LTR clades are described from C. intestinalis. The ascidian elements showed conservation of both the reverse transcriptase coding sequence and the overall structural organization seen in each clade. The apurinic/apyrimidinic endonuclease and nucleic-acid-binding domains encoded upstream of the reverse transcriptase, and the RNase H and the restriction enzyme-like endonuclease motifs encoded downstream of the reverse transcriptase were identified in the corresponding Ciona families.
  
  
  CONCLUSIONS
  The genome of C. intestinalis harbors representatives of at least five clades of non-LTR retrotransposons. The copy number per haploid genome of each element is low, less than 100, far below the values reported for vertebrate counterparts but within the range for protostomes. Genomic and sequence analysis shows that the ascidian non-LTR elements are unmethylated and flanked by genomic segments with a gene density lower than average for the genome. The analysis provides valuable data for understanding the evolution of early chordate genomes and enlarges the view on the distribution of the non-LTR retrotransposons in eukaryotes.
authors: Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Av Diagonal 645, E-08028 Barcelona, Spain.
authors: Jon
authors: J
authors: Permanyer
authors: Roser
authors: R
authors: Gonzàlez-Duarte
authors: Ricard
authors: R
authors: Albalat
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015139:Blotting, Southern; D002938:Ciona intestinalis / Q000235:genetics*; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D018628:Gene Dosage; D016678:Genome; D008969:Molecular Sequence Data; D010802:Phylogeny; D012194:RNA-Directed DNA Polymerase / Q000235:genetics; D018626:Retroelements / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D020079:Terminal Repeat Sequences / Q000235:genetics
chemical_list: D018626:Retroelements; D004247:DNA; D012194:RNA-Directed DNA Polymerase