PROKARYOTIC TRANSLATION INITIATION-FACTOR IF3 IS AN ELONGATED PROTEINCONSISTING OF 2 CRYSTALLIZABLE DOMAINS

We show that translation initiation factor IF3 can be split into two f ragments of nearly equal size by the Escherichia coli outer membrane p rotease omptin. Circular dichroism and small-angle neutron scattering show that the two fragments are structured as domains. Each domain is relatively compact, and they are separated by about 45 Angstrom in int act IF3. Thus IF3 is an elongated protein that consists of two well-se parated domains. We suggest that these two domains are involved in rib osome binding across the cleft of the 30S ribosome. We also report the crystallization of each domain of IF3.