retrotransposables

Retrotransposons are genetic elements that can move within a genome by copying themselves first into RNA and then back into DNA, a process called retrotransposition. This RNA-mediated transposition distinguishes them from DNA transposons, which move through a cut-and-paste mechanism. Retrotransposons are widespread in eukaryotes and can contribute significantly to genome size and structural variation.

Most retrotransposons are classified into two broad classes: long terminal repeat (LTR) retrotransposons and non-LTR retrotransposons. LTR retrotransposons resemble retroviruses in their life cycle and typically encode proteins for reverse transcription, integration, and sometimes proteolysis. Notable examples include elements related to Ty and Copia in fungi and plants and Gypsy elsewhere. Non-LTR retrotransposons include LINEs (long interspersed elements) and SINEs (short interspersed elements); LINEs are autonomous, encoding proteins needed for their own reverse transcription and insertion, while many SINEs are non-autonomous and rely on LINE-encoded machinery for mobilization. In humans, LINE-1 (L1) elements and SINEs such as Alu elements are prominent examples.

Retrotransposons can influence genomes by creating insertions, duplications, and rearrangements, altering gene expression, and contributing to exon shuffling and regulatory innovation. Their activity is tightly regulated by epigenetic mechanisms and small RNA pathways to limit genomic damage. Over evolutionary time, retrotransposons have shaped genome architecture, content, and evolution across diverse lineages, while remaining a subject of study for understanding genome dynamics and stability.