Spliceosome's core exposed

Abstract

The spliceosome complex removes intron sequences from RNA transcripts to form messenger RNA. The structure of a spliceosomal protein, Prp8, reveals the complex's active site and casts light on the origin of splicing. See Article p.638 The core of the spliceosome, a complex that removes introns from precursor mRNA transcripts prior to their expression, consists of several RNA–protein complexes arranged on the pre-mRNA. Prp8 is a protein in one such core complex, the U5 snRNP, and it contains the active site where cleavage occurs. Kiyoshi Nagai and colleagues have solved the structure of a large fragment of Prp8 bound to a U5 snRNP assembly factor, Aar2. This structure offers insight into how the splice sites might fit into the active site, and supports a possible unified evolutionary origin of eukaryotic pre-mRNA and bacterial group II intron-splicing mechanisms.