Introni

Introni, known in English as introns, are non-coding segments within genes that are transcribed into precursor messenger RNA but removed during RNA processing to produce mature messenger RNA. They interrupt protein-coding sequences (exons) and can vary greatly in length among organisms and even among genes within a genome.

Most introns in eukaryotes are spliceosomal introns, removed by a multi-component spliceosome composed of small nuclear RNAs and proteins. Some organisms also possess self-splicing introns, group I and II, which catalyze their own excision without a protein complex. In archaea and bacteria, introns are rare or restricted to certain RNA genes and mobile elements.

Introns influence gene expression beyond being removed. They enable alternative splicing, producing multiple protein isoforms from a single gene, and can harbor regulatory elements, noncoding RNAs, or conserved sequences that affect transcription, RNA stability, or translation. Intron-mediated enhancement is a described phenomenon where introns can increase gene expression.

Evolutionarily, introns are widespread in eukaryotes but largely absent in prokaryotes; their origins and turnover are topics of ongoing research. In many lineages, introns have been gained and lost over time, with conservation of some intron positions across distant species, suggesting functional constraints.

Mutations affecting splice sites, branch points, or regulatory elements can cause mis-splicing and disease. Introns are also a focus of genome annotation and RNA sequencing studies, which aim to identify splice variants and understand their biological roles.