Stringent control of RNA synthesis in the absence of guanosine 5'-diphosphate-3'-diphosphate.

Severe curtailment of RNA synthesis and widespread readjustment of cellular activities, together with an increase of guanosine 5'-diphosphate-3'-diphosphate (ppGpp) have been demonstrated in Escherichia coli cells starved for amino acid or energy. The rates of growth and RNA synthesis are reduced by shifting the growth temperature from 40 degrees C to 20 degrees C. The intracellular pool of ppGpp diminishes under such conditions. Furthermore, the accumulation of ppGpp normally attainable by either amino acid- or energy-limitation can be totally blocked by a downshift of temperature imposed prior to the starvation. However, the synthesis of stable RNA is still stringently restricted under these conditions. Two other nucleotides were also effected. The intracellular level of phantom spot (Gallant, J., Shell, L., and Bittner, R. (1976) Cell 7, 75-84) decreased upon temperature fall. Guanosine 5'-diphosphate-3'-monophosphate, whose concentrations have been linked to stringent response and stable RNA synthesis, did not change by the simple temperature downshift, but increased following amino acid limitation even when a downshift of temperature was imposed before the starvation. These results suggest that ppGpp is not always needed for inhibition of stable RNA synthesis during stringent response, and that a compound such as guanosine 5'-diphosphate-3-monophosphate may be involved in the stringent regulation of stable RNA synthesis, at least under the temperature downshift conditions.