Structural studies of an essential spliceosomal component Prp19

Pre-mRNA splicing is an essential step of gene expression, in which non-coding sequences called introns are removed from the pre-mRNA and the coding sequences named exons are ligated to form a mature mRNA. Splicing occurs on the spliceosome, a multi-Megadalton machinery that assembles step-wise on the pre-mRNA substrate, first as an inactive particle. Subsequently, the spliceosome undergoes dramatic compositional and conformational changes that lead to the formation of an active center able to catalyze the chemistry of splicing. The highly conserved splicing factor Prp19 is a scaffold of the so-called Nineteen complex (NTC) - a large building block of the spliceosome that is essential for the formation of the spliceosomal catalytic center, both in yeast and human. Prp19 forms a tetramer of about 220kDa in vivo and in vitro and its quaternary structure is essential for Prp19 function as a protein scaffold. To advance our understanding about the role of Prp19 as a tetrameric scaffold of the NTC, we decided to characterize its 3D structure by X-ray crystallography. The crystal structure of Prp19 tetrameric core reveals how a long quadruple coiled-coil sequesters the four U-box domains. Further analysis of the full-length Prp19 as well as of its tetrameric core by small-angle X-ray scattering are fully consistent with the crystallographic analysis and the previously published EM analysis. This work elucidates the quaternary structure of a multifunctional protein.