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.