Abstract: Provided herein, among other things, is an RNA that comprises a first exon, a second exon, a third exon and a fourth exon, wherein the RNA is capable of being spliced into; i. a first splicing product comprising the second exon or ii. a splicing second product comprising the third exon, wherein: i. an intron of the RNA, e.g., the intron between the first and second exons of the RNA, comprises an aptamer and ii. binding of a ligand to the aptamer determines whether the RNA is spliced into the first splicing product or the second splicing product. Methods and cells containing the RNA are also described.