STRUCTURE OF 5S RIBOSOMAL-RNA WITHIN THE ESCHERICHIA-COLI RIBOSOME - IODINE-INDUCED CLEAVAGE PATTERNS OF PHOSPHOROTHIOATE DERIVATIVES

The protection patterns of 5S rRNA in solution, within the ribosomal 5 0S subunit, 70S ribosomes, and functional complexes, were assessed wit h the phosphorothioate method. About 20% of the analyzed positions (G9 -G107) showed strong assembly defects: A phosphorothioate at one of th ese positions significantly impaired the incorporation of 5S rRNA into 50S particles. The reverse has also been observed: A phosphorothioate is preferred over a phosphate residue in the assembly process at a fe w positions. The results further demonstrate that 5S rRNA undergoes co nformational changes during the assembly in the central protuberance o f the 50S subunit and upon association with the small ribosomal subuni t forming a 70S ribosome. In striking contrast, when the 70S ribosomes are once formed, the contact pattern of the 5S rRNA is the same in va rious functional states such as initiation-like complexes and pre- and posttranslocational states.