Secondary structure features of ribosomal RNA species within intact ribosomal subunits and efficiency of RNA-protein interactions in thermoacidophilic (Caldariella acidophila, Bacillus acidocaldarius) and mesophilic (Escherichia coli) bacteria (original) (raw)

1983, Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression

Ribosomal subunits of Caldariella acidophila (max.growth temp., 90°C) have been compared to subunits of Bacillus acidocaldarius (max. growth temp., 70°C) and Escherichia coli (max. growth temp., 470C) with respect to (a) bihelical content of rRNA; (b) G-C content of bihelical domains and (c) tightness of rRNA-protein interactions. The principal results are as follows. 1. Subunits of C. acidophila ribosomes (T m = 90-93°C) exhibit considerable thermal tolerance over their B. acidocaldarius (T m --77°C) and E. coli counterparts (T m = 720C). 2. Based on the 'melting' hyperchromicities of the intact ribosomal subunits a 51-55% fraction of the nucleotides appears to participate in hydrogen-bonded base pairing regardless of ribosome source, whereas a larger fraction, 67-70%, appears to be involved in hydrogen bonding in the naked rRNA species. 3. The G-C content of bihelical domains of both free and ribosome-bound rRNA increases with increasing thermophily; based on hyperchromicity dispersion spectra of intact subunits and free rRNA, the bihelicai parts of C. acidophila rRNA are estimated to contain 63-64% G. C, compared to 58.5% G. C for B. acidocaldarius and 55% G.C for E. coli. 4. The increment in ribosome T m values with increasing thermophily is greater than the increase in T m for the free rRNA, indicating that within ribosomes bihelical domains of the thermophile rRNA species are stabilized more efficiently than their mesophile counterparts by proteins or/and other component(s). 5. The efficiency of the rRNA-protein interactions in the mesophile and thermophile ribosomes has been probed by comparing the releases, with LiCl-urea, of the rRNA species from the corresponding ribosomal subunits stuck to a Celite column through their protein moiety; it has been established that the release of C. acidophila rRNA from the Celite-bound ribosomes occurs at salt-urea concentrations about 4-fold higher than those required to release rRNA from Celite-bound E. coli ribosomes. 6. Compared to E. coli, the C. acidophila 50 and 30 S ribosomal subunits are considerably less susceptible to treatment designed to promote ribosome unfolding through depletion of magnesium ions. Abbreviations: RS, ribosomal subunit; L-rRNA and S-rRNA, RNA species obtained from the large and the small ribosomal subunits, respectively; SDS, sodium dodecyl sulphate.