Jürgen Schmitz ^{1, 3}, Gennady Churakov ¹, Hans Zischler ², and Jürgen Brosius ¹

¹ Institute of Experimental Pathology (ZMBE), University of Muenster, D-48149 Muenster, Germany;
² Institute of Anthropology, Johannes Gutenberg-University, D-55099 Mainz, Germany

³ Corresponding author.
E-MAIL:    jueschm@uni-muenster.de      FAX:  + 49-251-8358512

In addition to their central function in protein biosynthesis, tRNAs also play a pervasive role in genome evolution and architecture because of their extensive ability to serve as templates for retroposition. Close to half of the human genome consists of discernible transposable elements, a vast majority of which are derived from RNA via reverse transcription and genomic integration. Apart from the presence of direct repeats (DRs) that flank the integrated sequence of retroposons, genomic integrations are usually marked by an oligo(A) tail. Here, we describe a novel class of retroposons that lack A-tails and are therefore termed tailless retropseudogenes. Analysis of ~2500 tRNA-related young tailless retropseudogene sequences revealed that they comprise processed and unprocessed (pre-)tRNAs, 3'-truncated in their loop regions, or truncated tRNA-derived SINE RNAs. Surprisingly, their mostly nonrandom integration is dependent on the priming of reverse transcription at sites determined by their 3'-terminal 2-18 nucleotides and completely independent from oligoadenylation of the template RNA. Thus, tailless retropseudogenes point to a novel, variant mechanism for the biogenesis of retrosequences.

[Supplemental material is available online at: http://www.genome.org/cgi/content/full/gr.2720104/DC1
and:
http://zmbe2.uni-muenster.de/expath/addmat/tailless_retropseudogenes1.htm
The sequence data from this study have been submitted to GenBank under accession nos. AY550309-AY550335. The following individuals kindly provided reagents, samples, or unpublished information as indicated in the paper: C. Roos.]

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