Many classes of transposons and retrotransposons have invaded and shaped the genomes of their metazoan hosts. Class I transposons (i.e. retrotransposons) include both elements which contain long terminal repeats (LTRs) and many others lacking LTRs.

Along with retroviruses, retrotransposons share a fundamental mechanism of mobilisation through reverse transcription of an RNA template, via enzymatic activity of a reverse transcriptase.

Unlike retroviruses, retrotransposons remain entirely intracellular during their life cycle. Several distinctive and overlapping genome defense mechanisms have been developed over evolutionary time, as host organisms have fought back against these mobile retroelements. The ongoing conflict between these myriad genomic parasites and their widespread host organisms has resulted in positive and deleterious consequences including exaptation, genomic deletions, certain diseases including cancers, and the generation of diversity probably including the formation of new species.

Further reading: Retroviruses: Molecular Biology, Genomics and Pathogenesis

Labels: Exaptation, Metazoan, retroelements, Retrotransposon, Retrotransposons, Transposon, Transposons