Word of the Week: Retrotransposons

By Nogas1974 (Own work) [CC BY-SA 4.0] (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons

Retrotransposons – also known as transposons via ribonucleic acid (RNA) intermediates, if you want to be technical about it – are found in the DNA of both plants (such as wheat and maize) and humans, and share many characteristics with their neighbouring transposons.

They are small components of DNA, which infiltrate the cytoplasm of cells and seek to multiply and reproduce themselves before moving onto the nucleus where the overall DNA of a chromosome is stored. Once there, they integrate themselves into the genetic material, thus becoming part of the overall genetic makeup of the chromosome to be copied and multiplied endlessly with all of the other aspects of the DNA.

All retrotransposons utilise a direct copying mechanism, whereby their elements are first transcribed into RNA, then converted back into identical DNA sequences using a process called reverse transcription, and then finally inserted into the genomes of target chromosomes – not a simple process in the slightest.

HIV is an example of a retrovirus which behaves in a similar way to a standard retrotransposon – albeit one which probably has a lot more destructive power.

This process of infiltration and reproduction may sound quite intimidating, especially when you consider that retrotransposons share a lot of structural characteristics and processes with retroviruses; indeed, HIV is an example of a retrovirus which behaves in a similar way to a standard retrotransposon – albeit one which probably has a lot more destructive power.

Don’t panic, though: retrotransposons aren’t inherently bad. The human protein Syncytin-1, for instance, is encoded by a retrotransposon, and is vital for human placental development, embryo attachment and growth in the womb.

There are two sub-classes of retrotransposons – long terminal repeat retrotransposons (LTR retrotransposons) and non-long terminal repeat retrotransposons (non-LTR retrotransposons) – each with their own classifications. Non-LTR retrotransposons, for instance, are divided into two subtypes: long interspersed elements (LINEs) and short interspersed elements (SINEs). Both of these have, in rare cases, been incorporated in novel genes and seen to produce evolved functionalities. Not so scary after all?

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