retroposition

Retroposition is a genetic process in which an RNA transcript is reverse-transcribed and inserted back into the genome, creating a copy of a gene that normally lacks introns. The resulting copies are often called processed pseudogenes, though some can become functional retrogenes if they acquire regulatory sequences and expression.

The mechanism typically involves reverse transcription supplied by a retrotransposon-encoded enzyme, most commonly LINE-1. A mature mRNA is reverse-transcribed into cDNA, which is then integrated at a new genomic location. The insertion generally generates short target-site duplications and may leave behind a polyadenylated tail. Because the source transcript lacks introns, the inserted copy is intronless relative to the original gene.

Genomic features of retroposition include intronless sequence, high sequence similarity to the parent gene, and, in many cases, little or no promoter or regulatory information at the insertion site. If the retrocopy is not transcriptionally active, it becomes a processed pseudogene. However, some retroposed copies can recruit regulatory elements or gain new promoters, allowing transcription and sometimes functional expression as a retrogene. Such retrogenes can acquire novel expression patterns or functions, contributing to genetic novelty.

Detection and study of retroposition rely on comparative genomics and sequence analysis: intronless copies with high similarity to a parent gene, presence of target-site duplications, and adjacent poly(A) remnants point to a retroposition event. Evolutionarily, retroposition contributes to gene family diversification and innovation, though most retrocopies are nonfunctional. Insertion events can occasionally disrupt genes or regulation, linking retroposition to potential disease processes.