Exon

An exon is a segment of a gene retained in mature RNA after RNA splicing removes introns. Exons can encode protein or contribute regulatory sequences.

RNA splicing: RNA processing that removes introns from a precursor transcript and joins retained segments. Splicing distinguishes retained exons from excised introns.
Pre-mRNA: The initial RNA transcript in eukaryotes before processing produces mature messenger RNA. Exons are identified within precursor transcripts before splicing.
Exon skipping: A splice pattern or therapeutic strategy that omits a selected exon from mature RNA. Skipping a disease-associated exon can restore a usable reading frame in some disorders.
Messenger RNA: An RNA molecule that carries protein-coding information from DNA to the translation machinery. Joined exons form the sequence of a mature messenger RNA.
Spliceosome: A complex of small nuclear RNAs and proteins that carries out most pre-mRNA splicing. This molecular machine recognizes splice sites and joins exons.
Coding sequence: The portion of a gene or transcript whose nucleotide sequence specifies a protein. Some exons contain coding sequence, but exon status does not require it.
Exome sequencing: DNA sequencing focused on protein-coding regions and nearby splice junctions. Exon annotations define much of the sequence targeted by exome sequencing.
Protein isoform: One of multiple protein forms produced from a gene through differences in sequence or processing. Alternative exon combinations can produce distinct protein isoforms.
Splice site: A sequence at an intron boundary that helps define where RNA splicing occurs. Its recognition establishes the boundaries of an exon.
Untranslated region: A transcribed region of messenger RNA that is not translated into protein. Exons can include untranslated regions at the transcript's ends.

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