A complex molecular machine, the spliceosome, ensures that the genetic information from the genome, after being transcribed into mRNA precursors, is correctly assembled into mature mRNA. Splicing is a basic requirement for producing proteins that fulfill an organism’s vital functions. Researchers at the Heidelberg University Biochemistry Center have succeeded for the first time in depicting a faultily “blocked” spliceosome at high resolution and reconstructing how it is recognized and eliminated in the cell.