Birth of a retroposon: the Twin SINE family from the vector mosquito Culex pipiens may have originated from a dimeric tRNA precursor

Mol Biol Evol. 2001 Jan;18(1):74-84. doi: 10.1093/oxfordjournals.molbev.a003721.


SINEs are short interspersed repetitive elements found in many eukaryotic genomes and are believed to propagate by retroposition. Almost all SINEs reported to date have a composite structure made of a 5' tRNA-related region followed by a tRNA-unrelated region. Here, we describe a new type of tRNA-derived SINEs from the genome of the mosquito Culex pipiens. These elements, called TWINs, are approximately 220 bp long and reiterated at approximately 500 copies per haploid genome. TWINs have a unique structure compared with other tRNA-SINEs described so far. They consist of two tRNA(Arg)-related regions separated by a 39-bp spacer. Other tRNA-unrelated sequences include a 5-bp leader preceding the left tRNA-like unit and a short trailer located downstream of the right tRNA-like region. This 3' trailer is a 10-bp sequence that is ended by a TTTT motif and followed by a polyA tract of variable length. The right tRNA-like unit also contains a 16-bp sequence which is absent in the left one and appears to be located in the ancestral anticodon stem precisely at a position expected for a nuclear tRNA intron. According to this singular structure, we hypothesize that the TWIN: SINE family originated from an unprocessed polymerase III transcript containing two tRNA sequences. We suggest that some peculiar properties acquired by this dicistronic transcript, such as a polyA tail and a 3' stem-loop secondary structure, promote its retroposition by increasing its chances of being recognized by a reverse transcriptase encoded elsewhere in the C. pipiens genome.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Consensus Sequence
  • Culex / genetics*
  • Diptera / genetics
  • Disease Vectors
  • Evolution, Molecular*
  • Gene Dosage
  • Genome
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • RNA, Transfer / genetics*
  • Sequence Homology, Nucleic Acid
  • Short Interspersed Nucleotide Elements / genetics*


  • RNA, Transfer

Associated data

  • GENBANK/AF282724
  • GENBANK/AF282725
  • GENBANK/AF282726
  • GENBANK/AF282727
  • GENBANK/AF282728
  • GENBANK/AF282729