Exploration of RNA 3 ' terminal locations in rat ribosome

The locations of the 3' ends of RNAs in rat ribosome were studied by a fluo rescence-labeling method combined with high hydrostatic pressure and agaros e electrophoresis. Under physiological conditions, only the 3' ends of 28 S and 5.8 S RNA in 80 S ribosome could be labeled with a high sensitive fluo rescent probe - fluorescein 5-thiosemicarbazide (FTSC), indicating that the 3' termini of 28 S and 5.8 S RNA were located on or near the surface of 80 S ribosome. The 3' terminus of 5 S RNA could be attacked by FTSC only in t he case of the dissociation of the 80 S ribosome into two subunits induced by high salt concentration (1 M KCl) or at high hydrostatic pressure, showi ng that the 3' end of 5 S RNA was located on the interface of two subunits. However, no fluorescence-labeled 18 S RNA could be detected under all the conditions studied, suggesting that the 3' end of 18 S RNA was either locat ed deeply inside ribosome or on the surface but protected by proteins. It w as interesting to note that modifications of the 3' ends of ribosomal RNAs including oxidation with NaIO4, reduction with KBH4 and labeling with fluor escent probe did not destroy the translation activity of ribosome, indicati ng that the 3' ends of RNAs were not involved in the translation activity o f ribosome.