Interaction of 5S RNA-L5 protein complex with 40S subunits in rat liver ribosomes

When rat liver 80S ribosomes or polysomes were dissociated into their subunits by EDTA-treatment, a 5S RNA-L5 protein complex was present in EDTA-derived small subunits, and released from the subunits by urea. The interaction of 5S RNP with the small subunits did not occur in the case of 80S couples formed from 40S and 60S subunits in the presence of Mg2+, indicating that the attachment of 5S RNP to EDTA-derived small subunits was not an artifact caused by the unfolding of the subunits. These results give direct evidence that 5S RNP is located at the interface between large and small subunits, and suggest that 5S RNP binds to the 40S subunit in the functioning polysomes, but not the 80S couples.