Abstract
When deprived of a carbon source, Escherichia coli induces the synthesis of a group of carbon starvation proteins. The degradation of proteins labeled during starvation was found to be an energy-dependent process which was inhibited by the addition of KCN and accelerated when cells were resupplied with a carbon source. The degradation of the starvation proteins did not require the ATP-dependent Lon protease or the energy-independent proteases protease I, protease IV, OmpT, and DegP. During starvation, mutants lacking either the ClpA or ClpP subunit of the ATP-dependent Clp protease showed a partial reduction in the degradation of starvation proteins. Strains lacking ClpP failed to increase degradation of starvation proteins when glucose was added to starving cells. The clpP mutants showed a competitive disadvantage compared with wild-type cells when exposed to repeated cycles of carbon starvation and growth. Surprisingly, the glucose-stimulated, ClpP-dependent degradation of starvation proteins did not require either the ClpA or ClpB protein. The patterns of synthesis of starvation proteins were similar in clpP+ and clpP cells. The clpP mutants had reduced rates of degradation of certain starvation proteins in the membrane fraction when a carbon source was resupplied to the starved cells.