retrotransposase

Retrotransposons are mobile genetic elements that propagate within genomes through a "copy-and-paste" mechanism, utilizing reverse transcription to generate DNA copies of their RNA transcripts. Unlike transposons, which move via a "cut-and-paste" process, retrotransposons rely on an enzyme called reverse transcriptase to convert their RNA into complementary DNA (cDNA), which is then integrated into new genomic locations. This process allows them to amplify themselves and spread throughout the host genome, contributing to genomic diversity and evolution.

Retrotransposons are classified into two major groups: long terminal repeat (LTR) retrotransposons and non-LTR retrotransposons. LTR retrotransposons, such as Ty elements in yeast and retroviruses, contain long terminal repeats flanking their coding sequences. These elements encode three essential proteins: gag (group-specific antigen), pol (polymerase, including reverse transcriptase), and env (envelope). Non-LTR retrotransposons, including LINE (Long Interspersed Nuclear Elements) and SINE (Short Interspersed Nuclear Elements), lack LTRs and often rely on host factors for mobility. LINEs encode reverse transcriptase and other proteins necessary for transposition, while SINEs, such as Alu elements in humans, typically lack coding capacity and depend on LINE-encoded proteins for mobilization.

Retrotransposons can disrupt genes, alter gene expression, or contribute to genomic instability when they insert into critical regions. However, they also play roles in shaping genome architecture, influencing gene regulation, and driving adaptive evolution. Some retrotransposons have been co-opted for cellular functions, such as providing regulatory elements or contributing to the expansion of gene families. The activity of retrotransposons is often suppressed by host mechanisms, including DNA methylation and small interfering RNAs, to maintain genomic integrity.

Studies of retrotransposons provide insights into genome evolution, disease mechanisms, and the dynamics of genetic variation. Their widespread presence in eukaryotic genomes highlights their significance as major contributors to genomic complexity and plasticity.