introncontaining

Intron-containing is an adjective describing genes, transcripts, or RNA molecules that include introns. In eukaryotic organisms, genes are typically transcribed into pre-mRNA that contains both exons and introns. The introns are noncoding sequences that are removed during RNA processing by the spliceosome, yielding mature mRNA composed of exons only. Introns can vary widely in size and number among genes and species. In contrast, intronless genes either lack introns or have had introns lost over evolution.

Splicing mechanism: The spliceosome recognizes consensus sequences at the 5' donor site, the branch point, and the 3' acceptor site, leading to intron excision and exon ligation; a lariat intermediate is formed. Alternative splicing allows the same pre-mRNA to produce multiple mRNA isoforms, increasing proteome diversity. Intron retention is a form of alternative splicing in which an intron remains in the mature mRNA, potentially affecting translation. Nonsense-mediated decay may target transcripts with premature stop codons introduced or retained due to splicing.

Functions and significance: Introns can harbor regulatory elements, influence transcription, mRNA export, and translation efficiency. They allow exon shuffling during evolution and contribute to gene regulation. They also provide sites for noncoding RNAs and may affect the kinetics of transcript processing.

Evolution: The presence of introns is a feature of many eukaryotic genomes. The evolution of introns is debated (introns-early versus introns-late); some lineages show extensive intron gain or loss.

In genomics and annotation, distinguishing intron-containing genes from intronless genes helps in understanding gene structure, expression dynamics, and potential regulatory complexity.