Maintaining the Amino Acid Supply Chain

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Science  23 Dec 2005:
Vol. 310, Issue 5756, pp. 1865
DOI: 10.1126/science.310.5756.1865g

The efficiency and fidelity of protein synthesis is a key factor in cellular survival under a variety of growth conditions. Now Vabulas and Hartl (p. 1960) show that, under conditions of acute restriction in amino acid supply, continued protein biogenesis in mammalian cells is maintained by proteasomal degradation of preexisting proteins. Amino acid deficiency leads to severe depletion of the intracellular amino acid pool within minutes of proteasome inhibition and, concomitantly, protein translation is impaired. Both nascent and newly synthesized polypeptides remain protected from proteasomal degradation. At most, only a few percent of polypeptides are immediately degraded upon synthesis, indicating that, in contrast to previous estimates, protein biogenesis is a highly efficient process.

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