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J Bacteriol. 1967 May; 93(5): 1521-1526
Copyright © 1967 American Society for Microbiology. All Rights Reserved.

Stability of Ribosomes and Ribosomal Ribonucleic Acid from Bacillus stearothermophilus¹

^a Department of Medicine, Columbia University College of Physicians and Surgeons, and the Medical Service, Francis Delafield Hospital, New York, New York 10032

ABSTRACT

After heating at 65 C, ribosomes isolated from Bacillus stearothermophilus were strikingly more heat-stable than comparable preparations from Escherichia coli when tested for ability to support polyuridylic acid-directed phenylalanine incorporation at 37 C. The stability of ribosomes was also determined by measurements of hyperchromicity at 259 mµ while heating them from 25 to 90 C. In standard buffer containing 0.01 M Mg⁺⁺, the T_m (temperature at the midpoint of total hyperchromicity) of E. coli and B. stearothermophilus ribosomes was 71 and 81 C, respectively. In a magnesium-free buffer, the T_m of E. coli and B. stearothermophilus ribosomes was 44 and 64 C, respectively. Putrescine (0.01 M) was more effective in stabilizing ribosomes from B. stearothermophilus than those from E. coli. Spermidine (0.001 M), on the other hand, was more effective in stabilizing ribosomes from E. coli than those from B. stearothermophilus. Melting curves of total ribosomal ribonucleic acid (rRNA) from E. coli and B. stearothermophilus revealed T_m values of 50 and 60 C, respectively. Putrescine stabilized thermophile rRNA, but had no effect on E. coli rRNA. Sucrose density gradients demonstrated that thermophile 23S ribonucleic acid was degraded during storage at –20 C; the 23S component from E. coli was stable under these conditions. The results are discussed in terms of the mechanism of ribosome heat stability and the role of the ribosome in governing the temperature limits for bacterial growth.

² Present address: Department of Biological Sciences, Hunter College of the City University of New York, New York, N.Y. 10021.

¹ A preliminary report of part of this work was presented at the 65th Annual Meeting of the American Society for Microbiology, Atlantic City, N.J., 25–29 April 1965 (Bacteriol. Proc., p. 31, 1965).