SUMMARY: The recovery of sp. S14 cells from energy- and nutrient-starvation was monitored after the addition of glucose minimal medium. Upshift experiments were done throughout a starvation period of 200 h to determine whether cells were more responsive to nutrient addition at the onset of starvation, or if the previously described programme of starvation-induced cellular reorganization had to be completed before cells could become committed to recovery following nutritional upshifts. The kinetics of macromolecular synthesis (RNA, protein and DNA), the rate of respiration and changes in median cell volume in response to nutritional upshifts at different times of starvation were examined. The relative rates of RNA and protein synthesis increased immediately upon addition of glucose minimal medium; the increase in protein synthesis was not dependent on a parallel increase in RNA synthesis, indicating that the starved cells may have an excess of protein synthesizing machinery, including stable RNA and functional ribosomes. The subsequent increase in the rate of DNA replication was initiated approximately 60 min before the first apparent cell division at approximately one doubling of the theoretical minimal cell volume (V). Two-dimensional gel electrophoresis was used to demonstrate the fate of starvation-specific proteins during the upshift, and also the synthesis of recovery-induced proteins that were not found in starving cells. Most starvation-inducible proteins were repressed immediately at the onset of the nutritional upshift, while 11 of the 21 recovery-induced proteins identified were expressed exclusively during the maturation phase and were subsequently repressed at the onset of regrowth. The possible role of such maturation-specific proteins in the rapid formation of a reproductive cell committed to growth and division is discussed.


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