Cassandra retrotransposons carry independently transcribed 5S RNA

Ruslan Kalendar, Jaakko Tanskanen, Wei Chang, Kristiina Antonius, Hanan Sela, Ofer Peleg, Alan H. Schulman

Research output: Contribution to journalArticlepeer-review


We report a group of TRIMs (terminal-repeat retrotransposons in miniature), which are small nonautonomous retrotransposons. These elements, named Cassandra, universally carry conserved 5S RNA sequences and associated RNA polymerase (pol) III promoters and terminators in their long terminal repeats (LTRs). They were found in all vascular plants investigated. Uniquely for LTR retrotransposons, Cassandra produces noncapped, polyadenylated transcripts from the 5S pol III promoter. Capped, read-through transcripts containing Cassandra sequences can also be detected in RNA and in EST databases. The predicted Cassandra RNA 5S secondary structures resemble those for cellular 5S rRNA, with high information content specifically in the pol III promoter region. Genic integration sites are common for Cassandra, an unusual feature for abundant retrotransposons. The 5S in each LTR produces a tandem 5S arrangement with an inter-5S spacing resembling that of cellular 5S. The distribution of 5S genes is very variable in flowering plants and may be partially explained by Cassandra activity. Cassandra thus appears both to have adapted a ubiquitous cellular gene for ribosomal RNA for use as a promoter and to parasitize an as-yet-unidentified group of retrotransposons for the proteins needed in its lifecycle.

Original languageEnglish
Pages (from-to)5833-5838
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number15
StatePublished - 15 Apr 2008


  • Genome evolution
  • Pol III
  • Transcription
  • Transposable element

ASJC Scopus subject areas

  • General


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