Far upstream element-binding protein 1 and RNA secondary structure both mediate second-step splicing repression

Significance Splicing of mRNA precursors occurs in two sequential transesterification steps. We characterize a highly unusual inhibition of splicing in which the reaction is blocked between the two steps. We demonstrate that RNA secondary structure and an exonic splicing silencer element (ESS) can independently mediate second-step splicing repression in vitro and cause exon exclusion in vivo. Importantly, we provide evidence that far upstream element-binding protein 1, a single-stranded DNA- and RNA-binding protein initially identified as a regulator ofMYC transcription and recently implicated in several cancers, binds the ESS and functions as a splicing regulator in vitro and in vivo.