SITES OF RIBOSOMAL-RNAS INVOLVED IN THE SUBUNIT ASSOCIATION OF TIGHT AND LOOSE COUPLE RIBOSOMES

It was demonstrated previously by kethoxal treatment studies that tigh t (TC) and loose (LC) couple ribosomes use different sites of the 16 S and 23 S RNAs for subunit association (Burma, D. P., Srivastava, A. K ., Srivastava, S., and Dash, D. (1985) J. Biol. Chem. 260, 10517-10525 ). To localize these sites, a number of oligodeoxynucleotides compleme ntary to the suspected sites of the 16 S and 23 S RNAs were synthesize d, and their binding to ribosomes and effects on subunit association w ere studied, Some of the probes inhibit the association of both TC and LC ribosomes, some inhibit the association of TC but not LC ribosomes , and some inhibit the association of LC but not TC ribosomes. It appe ars that both TC and LC ribosomes use one common site of association, bases 818-823 of the 16 S and 2308-2313 of the 23 S RNA. The second si te, 788-793 of the 16 S RNA and 2753-2758 of the 23 S RNA for TC ribos omes, and 783-791 of the 16 S RNA and 2295-2303 of the 23 S RNA for LC ribosomes, is not shared. This suggests a spatial movement of the rib osomal subunits with respect to one another and lends further support to the model of translocation based on the interconversion of TC and L C ribosomes.