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R5 retrotransposons insert into a family of infrequently transcribed 28S rRNA genes of planaria.
Mol Biol Evol. 2003 Aug; 20(8):1260-70.MB

Abstract

A small (100 bp) region of the 28S rRNA gene has been shown to serve as the target site for the insertion of non-long terminal repeat (non-LTR) retrotransposons in both arthropods and nematodes. Here we characterize a lineage of non-LTR retrotransposons that inserts into this target site in the phylum Platyhelminthes. Dugesiid planaria contain elements, named R5, that insert 8 bp upstream of the target site used by arthropod R2 elements. The complete sequence of this element from Girardia tigrina revealed that it encoded two open reading frames (ORFs). The second ORF contained reverse transcriptase and restriction enzyme-like endonuclease domains similar to those found in R2 and R4, the elements that insert into the 28S genes of nematodes. The closest relative of R5, however, was the element NeSL-1, which inserts into the spliced leader 1 exons of nematodes. The rRNA genes of dugesiid planaria are unusual in that they comprise two types of rDNA units that differ by 8%-10% in nucleotide sequence of the 18S and 28S coding regions. Type II units are transcribed in adult tissues at levels that are less than 1% that of the type I units. R5 elements were only found inserted in the type II units, where presumably they cause less harm to the host. A second unusual aspect of the dugesiid rRNA genes is that the target site for the R5 insertion is duplicated 300 bp upstream of the original insertion site. R5 elements were identified at both sites. These findings expand the distribution of non-LTR elements that are specialized for insertion into the 28S gene and suggest that still more elements exist in other eukaryotic taxa. Attempts to trace the phylogeny of R5 did not offer sufficient resolution to determine whether R2, R4, and R5 represent the same lineage or whether they represent independent specializations for the 28S gene.

Authors+Show Affiliations

Department of Biology, University of Rochester, USA.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

12777502

Citation

Burke, William D., et al. "R5 Retrotransposons Insert Into a Family of Infrequently Transcribed 28S rRNA Genes of Planaria." Molecular Biology and Evolution, vol. 20, no. 8, 2003, pp. 1260-70.
Burke WD, Singh D, Eickbush TH. R5 retrotransposons insert into a family of infrequently transcribed 28S rRNA genes of planaria. Mol Biol Evol. 2003;20(8):1260-70.
Burke, W. D., Singh, D., & Eickbush, T. H. (2003). R5 retrotransposons insert into a family of infrequently transcribed 28S rRNA genes of planaria. Molecular Biology and Evolution, 20(8), 1260-70.
Burke WD, Singh D, Eickbush TH. R5 Retrotransposons Insert Into a Family of Infrequently Transcribed 28S rRNA Genes of Planaria. Mol Biol Evol. 2003;20(8):1260-70. PubMed PMID: 12777502.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - R5 retrotransposons insert into a family of infrequently transcribed 28S rRNA genes of planaria. AU - Burke,William D, AU - Singh,Daljit, AU - Eickbush,Thomas H, Y1 - 2003/05/30/ PY - 2003/6/5/pubmed PY - 2004/4/17/medline PY - 2003/6/5/entrez SP - 1260 EP - 70 JF - Molecular biology and evolution JO - Mol. Biol. Evol. VL - 20 IS - 8 N2 - A small (100 bp) region of the 28S rRNA gene has been shown to serve as the target site for the insertion of non-long terminal repeat (non-LTR) retrotransposons in both arthropods and nematodes. Here we characterize a lineage of non-LTR retrotransposons that inserts into this target site in the phylum Platyhelminthes. Dugesiid planaria contain elements, named R5, that insert 8 bp upstream of the target site used by arthropod R2 elements. The complete sequence of this element from Girardia tigrina revealed that it encoded two open reading frames (ORFs). The second ORF contained reverse transcriptase and restriction enzyme-like endonuclease domains similar to those found in R2 and R4, the elements that insert into the 28S genes of nematodes. The closest relative of R5, however, was the element NeSL-1, which inserts into the spliced leader 1 exons of nematodes. The rRNA genes of dugesiid planaria are unusual in that they comprise two types of rDNA units that differ by 8%-10% in nucleotide sequence of the 18S and 28S coding regions. Type II units are transcribed in adult tissues at levels that are less than 1% that of the type I units. R5 elements were only found inserted in the type II units, where presumably they cause less harm to the host. A second unusual aspect of the dugesiid rRNA genes is that the target site for the R5 insertion is duplicated 300 bp upstream of the original insertion site. R5 elements were identified at both sites. These findings expand the distribution of non-LTR elements that are specialized for insertion into the 28S gene and suggest that still more elements exist in other eukaryotic taxa. Attempts to trace the phylogeny of R5 did not offer sufficient resolution to determine whether R2, R4, and R5 represent the same lineage or whether they represent independent specializations for the 28S gene. SN - 0737-4038 UR - https://www.unboundmedicine.com/medline/citation/12777502/R5_retrotransposons_insert_into_a_family_of_infrequently_transcribed_28S_rRNA_genes_of_planaria_ L2 - https://academic.oup.com/mbe/article-lookup/doi/10.1093/molbev/msg141 DB - PRIME DP - Unbound Medicine ER -