EUKARYOTIC INITIATION FACTOR-III DOES NOT PREVENT ASSOCIATION THROUGH PHYSICAL BLOCKAGE OF THE RIBOSOMAL-SUBUNIT SUBUNIT INTERFACE

The "native" 40 S ribosomal subunit, in which the protein eukaryotic initiation factor 3 is bound to the 40 S small ribosomal subunit, has been reconstructed to 48 Å resolution. Comparison with a previous three-dimensional reconstruction of the "derived" 40 S subunit lacking any non-ribosomal components reveals the attachment site and morphology of the factor. It is a large (~165 to 170 Å long), bilobed, elongate structure, attached to the back lobes of the 40 S subunit by two strand-like features. Significantly, the factor is oriented away from the 60 S-subunit-40 S-subunit interface surface of the 40 S particle, suggesting that its anti-association activity is not accomplished via simple physical blockage of that surface. © 1992.