LTR retrotransposon

A. Genetic structure of LTR-retrotransposons (gypsy-type). B. Mechanism of retrotransposition, occurring inside viral-like particles in the cytoplasm. Reverse transcription initiates at a host tRNA primer binding site (PBS) located immediately downstream of the 5’LTR. The newly synthesized minus-strand cDNA copy of the 5’LTR is then transferred to the 3’LTR and used as a primer for reverse-transcription of the entire minus-strand sequence. An RNase H-resistant polypurine tract then serves as a primer for plus-strand synthesis of the 3’LTR and complementary PBS. The newly synthesized plus-strand PBS then associates with the already-synthesized minus-strand PBS, and double-stranded cDNA is finally produced. Double-stranded cDNA is then transferred to the nucleus by integrase proteins, and a new copy is integrated into the genome.

LTR retrotransposons are class I transposable elements (TEs) characterized by the presence of long terminal repeats (LTRs) directly flanking an internal coding region. As retrotransposons, they mobilize through reverse transcription of their mRNA and integration of the newly created cDNA into another genomic location. Their mechanism of retrotransposition is shared with retroviruses, with the difference that the rate of horizontal transfer in LTR-retrotransposons is much lower than the vertical transfer by passing active TE insertions to the progeny. LTR retrotransposons that form virus-like particles are classified under Ortervirales.

Their size ranges from a few hundred base pairs to 30 kb, the largest species reported to date are members of the Burro retrotransposon family in Schmidtea mediterranea.[1]

In plant genomes, LTR retrotransposons are the major repetitive sequence class constituting more than 75% of the maize genome.[2] LTR retrotransposons make up about 8% of the human genome and approximately 10% of the mouse genome.[3]

  1. ^ Grohme, Markus Alexander; Schloissnig, Siegfried; Rozanski, Andrei; Pippel, Martin; Young, George Robert; Winkler, Sylke; Brandl, Holger; Henry, Ian; Dahl, Andreas; Powell, Sean; Hiller, Michael; Myers, Eugene; Rink, Jochen Christian (January 2018). "The genome of Schmidtea mediterranea and the evolution of core cellular mechanisms". Nature. 554 (7690): 56–61. doi:10.1038/nature25473. hdl:21.11116/0000-0003-F5F3-6. ISSN 1476-4687.
  2. ^ Baucom, RS; Estill, JC; Chaparro, C; Upshaw, N; Jogi, A; Deragon, JM; Westerman, RP; Sanmiguel, PJ; Bennetzen, JL (November 2009). "Exceptional diversity, non-random distribution, and rapid evolution of retroelements in the B73 maize genome". PLOS Genetics. 5 (11): e1000732. doi:10.1371/journal.pgen.1000732. PMC 2774510. PMID 19936065.
  3. ^ McCarthy EM, McDonald JF (2004). "Long terminal repeat retrotransposons of Mus musculus". Genome Biol. 5 (3): R14. doi:10.1186/gb-2004-5-3-r14. PMC 395764. PMID 15003117.