It has been possible to demonstrate the complete absence of either charged tRNA(Glu) or charged tRNA(Val) at 42 degrees by the use of two stringent strains of E. coli, one temperature-sensitive for glutamyl-tRNA synthetase and the other temperature-sensitive for valyl-tRNA synthetase. In both strains, stable RNA synthesis ceases, and guanosine tetraphosphate accumulates upon incubation at the nonpermissive temperature. Unique among a series of antibiotics tested, only tetracycline was able to stimulate stable RNA synthesis and to cause disappearance of the guanosine nucleotide. In this regard tetracycline and the "relaxed" gene product appear to be analogous.