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Stimulation of Ribonucleic Acid Synthesis by Chloramphenicol in a rel+ Aminoacyl-Transfer Ribonucleic Acid Synthetase Mutant of Escherichia coli

Escherichia coli strain 9D3 possesses a highly temperature-sensitive valyl-transfer ribonucleic acid (tRNA) synthetase (EC 6.1.1.9). Since 9D3 is a rel+ strain, it cannot carry out net RNA synthesis at high temperature. A 100-μg amount of chloramphenicol (CAP) per ml added in the absence of valine cannot stimulate RNA synthesis. Either 300 μg of CAP or 100 μg of CAP plus 50 μg of valine per ml, however, promotes nearly maximal RNA synthesis. These results can be understood as follows. (i) Valyl-tRNA is required for net RNA synthesis, (ii) the synthetase lesion is incomplete, (iii) the rate of mutant acylation of tRNAval at high temperature is valine-dependent, and (iv) the CAP concentration determines the rate of residual protein synthesis. Data are also presented which demonstrate that the rate of net RNA synthesis can greatly increase long after the addition of CAP, if the amount of valyl-tRNA increases.