Regulated pre-mRNA splicing: The ghostwriter of the eukaryotic genome

► Two simple and consecutive chemical reactions are catalyzed co-trancriptionally by the spliceosome, a large macromolecular complex. ► The spliceosome is essential for generating mature mRNA. ► The cell takes advantage of this to generate different amounts and isoforms of mRNAs, according to its needs. ► In yeast, control of pre-mRNA splicing of critical genes allows the cell to affect all the pathways in gene expression. ► The spliceosome can be both the sensor and controller to fine tune genetic output.