U1 snRNA rewrites the "script".

Merkhofer, Evan C; Johnson, Tracy L · Cell · 2012

basic_science · Level V

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Abstract

Expression of eukaryotic mRNAs requires the collaboration of a host of RNA processing factors acting upon the transcript. Berg et al. describe how a pre-mRNA splicing factor modulates the activity of the polyadenylation machinery to regulate mRNA length, with important implications for isoform expression in activated neuronal and immune cells.