IMMUNOELECTRON MICROSCOPIC LOCALIZATION OF RIBOSOMAL-PROTEINS BS8, BS9, BS20, BL3 AND BL21 ON THE SURFACE OF 30S AND 50S SUBUNITS FROM BACILLUS-STEAROTHERMOPHILUS

The locations of ribosomal proteins BS8, BS9 and BS20 on the 30S subun it of Bacillus stearothermophilus ribosomes, and of BL3 and BL21 on th e 50S subunit, were determined by immunoelectron microscopy. BL3 was f ound to lie half-way down the body of the 50S subunit on the interface side, below the L7/L12 stalk, in agreement with the placement of the corresponding protein in Escherichia coli by neutron-scattering; BL21 was located at a similar position on the solvent side of the subunit, as predicted by cross-linking experiments with E. coli ribosomes. Simi larly, BS8 was found in the upper region of the body of the 30S subuni t on the solvent side, and BS9 on the top of the head of the subunit. also on the solvent side, both positions being in good agreement with neutron-scattering data and other immunoelectron microscopy results. I n contrast, BS20 was found to lie at the extreme base of the body of t he 30S subunit; this placement is not compatible with the location of E. coli S20 by neutron-scattering but fits very plausibly with other b iochemical data, such as sites of RNA-protein footprinting on 16S RNA, relating to the location of S20 in E. coli.