Analysis of the 5' junctions of R2 insertions with the 28S gene: implications for non-LTR retrotransposition

R2 elements are non-long terminal repeat retrotransposable elements that insert into 28S rRNA genes of most insect species. The single open reading frame of R2 encodes a protein with both endonuclease activity, which cleaves the target site, and reverse transcriptase activity, which uses this cleava...

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Bibliographic Details
Published in:Genetics (Austin) 1996-03, Vol.142 (3), p.853-863
Main Authors: George, J.A, Burke, W.D, Eickbush, T.H
Format: Article
Language:English
Subjects:
Animals
Base Sequence
deletions
DNA Transposable Elements
DNA, Ribosomal
Drosophila
Drosophila - genetics
Drosophila melanogaster
Drosophila melanogaster - genetics
genes
Genes, Insect
genetic change
genetic variation
Genetics
Insects
Investigations
Molecular Sequence Data
mutation
nucleases
nucleotide sequences
retrotransposons
Ribonucleic acid
ribosomal DNA
ribosomal RNA
RNA
RNA, Ribosomal, 28S
RNA-directed DNA polymerase
Sequence Homology, Nucleic Acid
species differences
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Summary:R2 elements are non-long terminal repeat retrotransposable elements that insert into 28S rRNA genes of most insect species. The single open reading frame of R2 encodes a protein with both endonuclease activity, which cleaves the target site, and reverse transcriptase activity, which uses this cleavage to prime reverse transcription. This target-primed reverse transcription mechanism is also used by group II introns. Little is known of the mechanism by which the 5' end of R2 is integrated after reverse transcription. We have determined the 5' junction sequence of 94 R2 elements from 14 different species of Drosophila. Only 37% of the full-length elements contained precise 5' junctions; the remainder contained deletions of the 28S gene and/or insertions of additional sequences. Because the 5' junctions of truncated copies were similar to full-length elements, no sequences at the 5' end of R2 appear to be required for element integration. A model in which the R2 reverse transcriptase is capable of switching templates from the R2 RNA transcript to the upstream 28S gene can best explain the observed 5' junction sequences. This template jumping is analogous to the template switching of retroviral reverse transcriptases during formation of the double-stranded integration products.
ISSN:0016-6731
1943-2631
1943-2631
DOI:10.1093/genetics/142.3.853