Guanosine-5‘-diphosphate-3‘-diphosphate (ppGpp) and the regulation of protein breakdown in Escherichia coli.
Year: 1980
Type: article
Abstract: Experiments were undertaken to clarify the role of guanosine-5'-diphosphate-3'-diphosphate (ppGpp) in regulating protein catabolism.To measure proteolysis over short periods, gel filtration was used to wash cells of labeled amino acids in a nontraumatic fashion.When relA'spoT' cells starving for amino acids were administered tetracycline to prevent ppGpp synthesis, the level of ppGpp decreased with a tlIz of 20 t o 30 s and the rate of protein breakdown decreased t o basal rates as fast as could be measured (within 1 or 2 min).In analogous experiments with relA'spoTcells which are defective in ppGpp degradation, ppGpp decayed with a t l / z of 9 to 15 min and proteolysis decreased only after 10 to 15 min.Thus, the high rate of proteolysis in starvation requires the continued presence of a high level of ppGpp.In cells starved for amino acids, the steady state level of ppGpp could be varied by using different amounts of tetracycline, which inhibited ppGpp synthesis only partially.The rate of proteolysis was proportional to the concentration of ppGpp.During exponential growth, relA'spoTcells contain more ppGpp and show a higher rate of catabolism than re1A'spoT'.This difference disappeared upon addition of tetracycline.Upon starvation for a carbon source, rates of proteolysis and levels of ppGpp increased in re1A'relX' strains.In relA-re" cells, however, ppGpp did not accumulate and protein degradation did not rise.In energy-restricted cells (relA'spoT'), tetracycline caused a reduction in ppGpp levels with a t l / ~ of 1.5 to 1.75 min and a fall in proteolysis to basal rates after 4 or 5 min.Thus, ppGpp seems to signal the acceleration of proteolysis during both amino acid and energy deprivation.However, under these two conditions, the dependence of protein degradative rates on ppGpp concentration differed.Thus, other factors besides ppGpp must also be involved in regulating this process.When Escherichia coli are starved for essential amino acids, an energy source, or certain inorganic ions, the average rate of degradation of cell proteins increases (1-3).This stimulation of protein degradation coincides with an inhibition in the starved cells of a number of important growth-related processes (2), including the synthesis of stable RNA (4-6), ribosomal proteins (7), phospholipids (8, 9) and nucleotide
Source: Journal of Biological Chemistry
Authors: R. Voellmy, A.L. Goldberg
Institutions: University of Geneva, Harvard University
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W1616921663