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Exon Junction Complex Electron Microscope Data
The three-dimensional arcitecture of the EJC core.
The exon junction complex (EJC) is a macromolecular complex deposited at splice junctions on mRNAs due to splicing. At the core of the EJC are four proteins: eIF4AIII, a member of the DExH/D-box family of NTP-dependent RNA binding proteins, Y14, Magoh, and MLN51. These proteins form a stable heterotetramer that remains bound to the mRNA throughout many different cellular environments. We have determined the three-dimensional (3D) structure of this EJC core using negative-stain random-conical tilt electron microscopy. This structure represents the first structure of a DExH/D-box protein in complex with its binding partners. The EJC core is a four-lobed complex with a central channel and dimensions consistent with its known RNA footprint of about ten nucleotides. Using known X-ray crystallographic structures and three of the four components, we propose a model for complex assembly on RNA and explain how Y14:Magoh may influence eIF4AIII's RNA binding.
Linked to the right is a reconstruction of the exon junction complex core (EJC) in MRC/CCP4 format at about 25 Å resolution. The reconstruction was calculated from 9,655 images of negatively stained particles collected at 120 kV on a Philips CM12 electron microscope at 60,000 magnification, resulting in a pixel size of 1.17 Å.