Ribosomes on the night shift

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Science  18 May 2018:
Vol. 360, Issue 6390, pp. 710-711
DOI: 10.1126/science.aat7121

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From an evolutionary perspective, life involves two simple goals: survival and reproduction. But these goals are fundamentally at odds. Reproduction depends on growth, but attempts to grow when nutrients are scarce can jeopardize survival. In cells, growth is accomplished in large part by ribosomes, huge RNA-protein machines that translate nucleic acid messages into protein, the main biochemical constituent of cells. In nutrient-rich conditions, cells can be filled with ribosomes; they comprise more than a third of total biomass in rapidly growing Escherichia coli (1). But what happens to ribosomes when nutrient levels decline, as occurs sporadically in microbes and nightly in sleeping humans? Biosynthesis subsides, and ribosomes now serve as a reservoir of nutrients. Building on recent progress probing the regulation of protein synthesis and degradation from Gu et al. (2) and Abu-Remaileh et al. (3), on page 751 of this issue, Wyant et al. (4) elucidate a pathway in which ribosomes are selectively digested, promoting survival in starved cells.