Cell Biology

Like Ps in a Pod

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Science  04 Jul 2008:
Vol. 321, Issue 5885, pp. 16
DOI: 10.1126/science.321.5885.16b

In the budding yeast, the 26S proteasome degrades many proteins involved in cell-cycle progression and thus is essential for cell proliferation. In actively growing yeast, 80% of the 26S proteasome, which comprises a 20S core particle and a 19S regulatory particle, is localized inside the nucleus. In quiescent cells, proteasome proteolytic activity decreases and correlates with release of the regulatory particle, but the fate of the disassembled subcomplexes remains unclear.

Laporte et al. found that when cells exhausted their carbon source and entered quiescence, subunits from the 20S and 19S particles colocalized into cytoplasmic foci termed proteasome storage granules (PSGs). Consistent with the proposal that PSGs act as storage depots, refeeding the cells resulted in rapid relocalization of proteasomes into the nucleus and did not require de novo protein synthesis. Other macromolecular assemblies triggered by quiescence have been described, such as P-bodies, which contain RNA and RNA-modifying proteins, suggesting that there may be a major reorganization of cellular structures upon entry into quiescence. — VV

J. Cell Biol. 181, 737 (2008).

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