U1-Mediated Exon Definition Interactions Between AT-AC and GT-AG Introns

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Science  08 Nov 1996:
Vol. 274, Issue 5289, pp. 1005-1008
DOI: 10.1126/science.274.5289.1005


A minor class of metazoan introns has well-conserved splice sites with 5′-AU-AC-3′ boundaries, compared to the 5′-GU-AG-3′ boundaries and degenerate splice sites of conventional introns. Splicing of the AT-AC intron 2 of a sodium channel (SCN4A) precursor messenger RNA in vitro did not require inhibition of conventional splicing and required adenosine triphosphate, magnesium, and U12 small nuclear RNA (snRNA). When exon 3 was followed by the 5′ splice site from the downstream conventional intron, splicing of intron 2 was greatly stimulated. This effect was U1 snRNA-dependent, unlike the basal AT-AC splicing reaction. Therefore, U1-mediated exon definition interactions can coordinate the activities of major and minor spliceosomes.