Exonintron

Exonintron is a term occasionally used to describe a region that includes an exon together with the immediately adjacent intronic sequences that flank it. It is not a universally standardized term in genetics, and most references refer to the distinct components—exons and introns—or to the exon–intron boundary rather than to a combined unit called an exonintron.

In a typical gene, exons are the portions that are transcribed and retained in the mature mRNA, encoding the amino acid sequence of a protein, while introns are transcribed but spliced out before translation. The boundary between an exon and an intron features conserved splicing signals, notably the 5' donor site and 3' acceptor site, as well as branch point sequences and a polypyrimidine tract. The spliceosome recognizes these signals to remove introns and join exons together during RNA processing.

Regulatory elements influencing splicing can reside in both exonic and intronic regions. Exonic splicing enhancers and silencers within exons, as well as intronic regulatory motifs, can affect whether an exon is included or skipped in the final mRNA. The context provided by neighboring intronic sequences can thus modulate exon recognition and alternative splicing outcomes.

Understanding exons, introns, and their boundaries remains central to studies of gene expression, genetic variation, and inherited diseases. While exonintron may appear in some educational or theoretical discussions, the standard concepts of exon, intron, and exon–intron junctions are the primary framework for describing gene architecture and RNA processing.