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Structure and Function of Transfer Ribonucleic Acid

III. SOME PROPERTIES OF A COMPLEX BETWEEN VALYL TRANSFER RIBONUCLEIC ACID SYNTHETASE AND TRANSFER RIBONUCLEIC ACID SPECIFIC FOR VALINE

From the ¹ From the Department of Medical Biochemistry, University of Gothenburg, Gothenburg, Sweden

The formation and some properties of a stable complex between valyl transfer ribonucleic acid synthetase and transfer RNA from yeast have been investigated by three different methods for the isolation of the complex: filtration over Sephadex, sucrose gradient centrifugation, and electrophoresis on Pevikon as supporting medium.

Transfer RNA specific for valine (tRNA^val) can be separated into two fractions, tRNA^valI and tRNA^valII, in the approximate proportions 3:1 by chromatography on DEAE-cellulose. With the Sephadex filtration technique only the minor fraction, tRNA^valII, gave a stable complex with the enzyme. When sucrose gradient centrifugation or electrophoresis was used it was possible to show the formation of stable complexes between the enzyme and both tRNA^valI and tRNA^valII. With the centrifugation technique complexes between the enzyme, AMP, valine, and valyl-tRNA could also be shown. This technique gave a separation of complex and free enzyme that permitted a determination of the molar ratio of tRNA^val to enzyme in the complex. The values obtained ranged from 0.7 to 0.9, indicating one tRNA-site per enzyme molecule. The centrifugation data also showed that only 50 to 60% of the enzyme molecules had the ability to form a stable complex with tRNA^valI while all of the enzyme could be obtained as a complex with tRNA^valII.

tRNA^val when present as a complex with the enzyme was protected against T₁-RNase under conditions in which free tRNA^val was completely inactivated. The protection against phosphodiesterase, although significant, was much less pronounced.

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