Segments containing a few nucleotides that reside at the ends of introns and function in excision and splicing reactions during the processing of transcripts from split genes. The sequence at the 5′ end of any intron transcript is called the donor junction and the sequence at the 3′ end the acceptor junction. U1 RNA (q.v.) contains a segment adjacent to its 5′ cap that exhibits complementarity to the sequences at the donor and acceptor splice junctions of introns. U1 binds to such segments, causing introns to loop into a lariat (q.v.) that allows intron excision and exon splicing. See Usn RNAs.
Subjects: Genetics and Genomics.