Structural insights into the exon junction complex

In higher eukaryotes, the exon junction complex is loaded onto spliced mRNAs at a precise position upstream of exon junctions, where it remains during nuclear export and cytoplasmic localisation until it is removed during the first translation round. The exon junction core complex consists of four proteins that form a dynamic binding platform for a variety of peripheral factors involved in mRNA metabolism. In the complex, mRNA binding is mediated by the DEAD-box protein eIF4AIII, and inhibition of its ATPase activity forms the mechanistic basis for the long-term stability of the complex. Recent crystal structures of the exon junction complex and eIF4AIII have provided the structural framework for investigating the function of the eIF4AIII ATPase and for localisation of surface patches involved in binding peripheral factors. Additionally, by comparison with the structure of a second DEAD-box protein also bound to RNA and ATP, general principles for the ATPase and unwinding/mRNP remodelling activities for this important group of enzymes can be proposed on the basis of atomic structures.