The protection patterns of 5S rRNA in solution,
within the ribosomal 50S subunit, 70S ribosomes, and functional
complexes, were assessed with the phosphorothioate method.
About 20% of the analyzed positions (G9–G107) showed
strong assembly defects: A phosphorothioate at one of these
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 few positions. The results
further demonstrate that 5S rRNA undergoes conformational
changes during the assembly in the central protuberance
of the 50S subunit and upon association with the small
ribosomal subunit 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 various functional states
such as initiation-like complexes and pre- and posttranslocational
states.