Stabilization of Ribosomal RNA in Archaeal Hyperthermophiles; 16S and 23S rRNAs from Sulfolobus solfataricus
Kathleen NOON*, Eveline BRUENGER, and James MCCLOSKEY
Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112
The structures and mechanisms of stabilization of ribosomal RNA in thermophiles is of recently recognized importance because of rapidly accumulating evidence that the RNA component of the ribsome, rather than protein, plays the principal role in protein biosynthesis (1). The archaeon S. solfataricus cultured at temperatures 60-80℃ has been studied as a model organism to provide the first complete census of posttranscriptionally modified residues (identities and levels) in 16S and 23S rRNA in any thermophile. 16S rRNA was found to contain 38 modified sites, and 50 sites occur in 23S rRNA (VS. 11 and 23, respectively, in E. coli), the highest modification levels thus far reported for any prokaryote. A total of ten different nucleosides were characterized by HPLC-mass spectrometry, with exceptional levels of nucleoside species methylated at 0-2' of ribose: 〜24 residues in 16S RNA and 43 in 23S RNA. These types of modifications have previously documented effects on regional polynucleotide chain stabilization (2) and melting temperature (3) resulting from thermodynamic preference for the more rigid C3'-endo ribose conformation. Several of the ribose-methylated derivatives increase in relative amount in response to increasing culture temperature over the range 60℃→83℃, e.g.: 2'-O-methyladenosine in 16S rRNA, 21% net increase; 2'-O-methylcytidine in 23S rRNA, 24% increase. The stabilizing role of posttranscriptional modifications in thermophile rRNA appears to be similar to that found in tRNA. However the extent of modification is less than in tRNA, which is attributed in part to the reduced necessity for stabilization due to the integral presence of numerous ribosomal proteins, in contrast to tRNA which is much less influenced by stabilizing intermolecular interactions during translation.
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3. Kowalak, J.A., Dalluge, J.J., McCloskey, J.A. and Stetter, K.O. (1994) Biochemistry, 33, 7869- 7876.
