HETERONUCLEAR NMR-STUDIES OF ESCHERICHIA-COLI TRANSLATION INITIATION-FACTOR IF3 - EVIDENCE THAT THE INTER-DOMAIN REGION IS DISORDERED IN SOLUTION

Initiation factor IF3 from Escherichia coli plays a critical role in t he selection of the correct initiation codon. This protein is composed of two domains, connected by a lysine-rich hydrophilic linker. The co nformation of native IF3 was investigated by heteronuclear NMR spectro scopy. The two domains are independent and show little or no interacti on. Heteronuclear relaxation studies of a sample selectively labelled on lysine residues demonstrates that the inter-domain Linker is highly flexible, exhibiting increased N-15 T-2 values and negative H-1{N-15} nuclear Overhause effects over a length of at least eight residues. A nalysis of the rotational correlation times further shows that the mot ions of the two domains are most Likely uncorrelated. The inter-domain linker thus displays almost totally unrestricted motions. Accordingly , the amide protons in the central region are shown to be in fast exch ange with water. Such a high degree of flexibility of the inter-domain linker might be required for IF3 domains to interact with distant reg ions of the ribosome. (C) 1997 Academic Press Limited.