Date of Award


Degree Type


University or Center

Atlanta University (AU)

Degree Name




First Advisor

Dr. Luther S. Williams


This study was undertaken to determine whether the for mation of leucyl-transfer ribonucleic acid synthetase (tRNA synthetase) was "constitutive11 in nature or was subjected to some control mechanism. The growth of wild type cultures in minimal-glucose medium supplemented with excess leucine, as compared to minimal-glucose medium, did not affect the specific activity of the leucine synthetase. Using an auxotroph for leucine, a shift of this culture from a medium containing excess leucine to restricting (growth rate) amounts of leucine, resulted in a significant increase in the specific activity of the leucyl-tRNA synthetase for the first hour of incubation. This indicated a derepression in the rate of formation of the enzyme. After the first hour of incubation, there was a decline in the rate of synthesis and some inactivation of this synthetase activity. Further studies provide results that the addition of leucine to the highly derepressed cultures caused repression of synthesis and halted the inactivation of the leucyl-tRNA synthetase. These results confirm previous findings indicating that the rate of formation of arginyl- and histidyl-tRNA synthetase was regulated, and suggest that the regulation of aminoacyltRNA synthetase formation follows a repression-like mechanism.

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