5 S RNA-protein complex is involved in ribosomal subunit association

The immobilized tRNA-50 S ribosomal subunit protein (TP50) complex binds the smaller ribosomal subunit. We constructed tRNA . TP50 . 5 S [32P] RNA and tRNA . TP50 . t [32P] RNA complexes and investigated the accessibility of the 32P-labelled tRNAs to ribonuclease T1. It was found that in this complex both 5 S RNA and tRNA are attacked by T1 RNase. In sharp contrast, the addition of 30 S subunit protects 5 S RNA as well as tRNA from degradation. We suggest that 5 S RNA-TP50 complex is exposed to the ribosomal interface and is involved in subunit interaction.