SOLUTION STRUCTURE OF THE RIBOSOME-BINDING DOMAIN OF ESCHERICHIA-COLITRANSLATION INITIATION-FACTOR IF3 - HOMOLOGY WITH THE U1A PROTEIN OF THE EUKARYOTIC SPLICEOSOME

Initiation of translation in prokaryotes requires the formation of a c omplex between the messenger RNA,the 30 S ribosomal subunit and the in itiator tRNA(fMet). Initiation factor IF3 binds to the 30 S ribosomal subunit and proof-reads the initiation complex, thereby ensuring the a ccuracy of this step. IF3 also plays a pleiotropic role in the regulat ion of translation, as a result of differential influences exerted on the levels of the initiation of translation of genes or groups of gene s. IF3 is composed of two independent domain or roughly identical size s. We have expressed and purified the C-terminal domain of E. coli IF3 and shown that it retains both the 30 S particle binding and 70 S rib osome dissociating activities of the native protein. We have obtained H-1 and N-15 NMR resonance assignments and its 3D solution structure w as calculated using 551 restraints. It is composed of a mixed beta-she et backed by two alpha-helices. It shows a striking resemblance to the U1A small nuclear ribonucleoprotein structure, which binds to the UI snRNA in the eukaryotic spliceosome. This suggests a convergent evolut ion process for these two proteins that are associated with ribonucleo proteic complexes. (C) 1995 Academic Press Limited