Abstract
This paper presents data on the physical and chemical properties of the ribosomes and RNA of Thermus aquaticus, an organism able to grow at temperatures up to 79°. Ultracentrifugal analysis of purified ribosomes in 0.01 M Mg 2+ demonstrated components sedimenting at 50 S, 70 S and 100 S. Chemical analysis of ribosomes revealed an average content of 59% protein and 41% RNA. When heated in standard buffer, Escherichia coli ribosomes began gradual dissociation at 59° with a T m of 71°. In contrast, T. aquaticus ribosomes were stable up to 79° and had a T m of 86°. T. aquaticus ribosomal RNA (rRNA) was found to be more thermal stable than that of E. coli. However, thermal denaturation profiles of fractionated 16-S and 23-S rRNA of E. coli and T. aquaticus demonstrated that only the 23-S species of T. aquaticus rRNA was more stable than that of E. coli. Thermal denaturation studies revealed that T. aquaticus transfer RNA (tRNA) was stable up to 68° and had a T m of 86°; whereas, E. coli tRNA was only stable up to 55° and had a T m of 80°. The rRNA and tRNA of T. aquaticus was higher in guanine and cytosine than similar components of E. coli. There was a striking correlation between the temperature at which denaturation of ribosomes of T. aquaticus initiates and the maximum growth temperature. These data provide further evidence for the heat stability of thermophilic macromolecules.
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