Protein Name

Exon Junction Complex



Biological Context

The exon junction complex (EJC) plays a major role in post-transcriptional regulation of mRNA in metazoa.
Expression of the proteins is composed of the transcription, translation, and post-transcriptional regulation in eukaryotes. In these processes, the precursor mRNA is spliced into the matured mRNA, and then, it is translated to a protein. This is an important biological event, especially in human cells, because it makes possible the production of diverse proteins from limited number of genes. All of the steps above are functionally coupled and are contributed to each other to effective gene expression. It is known that some cytoplasmic events to mRNA, such as polyadenylation and capping, can influence the metabolism of RNA products. In addition, the pre-mRNA splicing also has a significant role in it. Other than the role of the splicing mentioned above, the splicing deposits a protein complex as a landmark on the transcript. This complex is called the exon junction complex. The EJC anchors other proteins, such as splicing coactivator and mRNA export factors, involved in the post-transcriptional regulation.

Structure Description


EJC is composed of four protein subunits, mRNA, and ATP. Four subunits are the following: elF4AIII (RNA helicase, yellow and red in Fig. 1), Barentsz (CASC3: cancer susceptibility candidate gene 3 protein, magenta), Mago (green), and Y14. (cyan)

Fig. 1 Overall Architecture of the EJC.

The overall architecture is an L-shaped structure (Fig. 1). The two domains in elF4AIII form a cleft, which binds to the ATP molecule (Fig. 2).

Fig. 2 The two domains in elF4AIII form a cleft.

RNA (blue in Fig. 1) binds to both of the two domains with a bent conformation. Barentsz does not take a globular fold but has an extended conformation. Shown in Fig. 1 is not the whole structure of Barentsz, but separated ones by experimental procedure. The interaction of Mago and Y14 is mediated by the α-helical surface of Mago and the β-sheet surface of the RNA binding domain of Y14. Both of these two proteins also interact with elF4AIII. Thus, the components of the EJC interact with each other and form an interaction network. The electrostatic interactions are involved in the network (Fig. 3). The network stabilizes the ATP binding mode in a cleft between the two domains in elF4AIII, anchoring Mago, Y14, and Barentsz with the interface of elF4AIII.

Fig. 3 Electrostatic interaction network

Protein Data Bank (PDB)



Bono, F. Ebert, J. Lorentzen, E. Conti, E.; "The crystal structure of the exon junction complex reveals how it maintains a stable grip on mRNA."; Cell(Cambridge,Mass.); (2006) 126:713-725 PubMed:16923391.


author: Daisuke Kuroda

Japanese version:PDB:2J0S