Emerging views about the molecular structure of the spliceosomal catalytic center.

Pre-mRNA splicing occurs in two chemical steps that are catalyzed by a large, dynamic RNA-protein complex called the spliceosome. Initially assembled in a catalytically inactive form, the spliceosome undergoes massive compositional and conformational remodeling, through which disparate RNA elements are re-configured and juxtaposed into a functional catalytic center. The intricate construction of the catalytic center requires the assistance of spliceosomal proteins. Recent structure-function analyses have demonstrated that the yeast-splicing factor Cwc2 is a main player that contacts and shapes the catalytic center of the spliceosome into a functional conformation. With this advance, corroborated by the atomic structure of the evolutionarily related group IIC introns, our understanding of the organization and formation of the spliceosomal catalytic center has progressed to a new level.