Ribosomal subunit antiassociation activity in rabbit reticulocyte lysates. Evidence for a low molecular weight ribosomal subunit antiassociation protein factor (M(r) = 25,000)

A ribosomal subunit antiassociation activity has been purified from both the postribosomal supernatant and ribosomal salt-wash protein fractions of rabbit reticulocyte lysates. A majority (> 90%) of the activity is associated with a low molecular weight protein of M(r) of approximately 25,000. A small but significant level of antiassociation activity (< 10%) was found to be associated with higher molecular weight protein fractions. The purified 25,000-dalton antiassociation factor interacts with 60 S ribosomal subunits to prevent them from reassociating with 40 S ribosomal subunits. The factor does not seem to interact directly with 40 S subunits nor does it dissociate 80 S monosomes. The properties of this factor are thus similar to the eukaryotic initiation factor 6 isolated from both wheat germ and calf liver extracts.