Mechanism for the initiation of spliceosome disassembly.

Precursor-mRNA (pre-mRNA) splicing requires the assembly, remodelling and disassembly of the multi-megadalton ribonucleoprotein complex called the spliceosome. Recent studies have shed light on spliceosome assembly and remodelling for catalysis, but the mechanism of disassembly remains unclear. Here we report cryo-electron microscopy structures of nematode and human terminal intron lariat spliceosomes along with biochemical and genetic data.