Intracellular protein and nucleic acid turnover in resting yeast cells

Abstract

In the absence of exogenous energy and nitrogen, resting yeast cells are capable of replenishing both their nucleotide and free amino acid pools. This replenishment phenomenon is the result of intracellular protein and nucleic acid breakdown rather than of cell lysis. Isotopically labeled cells showed turnover rates of 6.6 · 10 −3 h −1 and 1.5 · 10 −3 h −1 for protein and nucleic acid respectively. Protein and nucleic acid degradation, as well as their synthesis, are energy-requiring reactions. When exogenous energy is available, the degradation products are reutilized for protein and nucleic acid synthesis. Employing 15N-purine-grown cells, it was found that the amino groups of nucleic acid purines can serve as nitrogen reservoirs for limited protein synthesis.