title: Cost of unneeded proteins in E. coli is reduced after several generations in exponential growth.
abstract: When E. coli cells express unneeded protein, they grow more slowly. Such penalty to fitness associated with making proteins is called protein cost. Protein cost is an important component in the cost-benefit tradeoffs that underlie the evolution of protein circuits, but its origins are still poorly understood. Here, we ask how the protein cost varies during the exponential growth phase of E. coli. We find that cells growing exponentially following an upshift from overnight culture show a large cost when producing unneeded proteins. However, after several generations, while still in exponential growth, the cells enter a phase where cost is much reduced despite vigorous unneeded protein production. We find that this reduced-cost phase depends on the ppGpp system, which adjusts the amount of ribosomes in the cell and does not occur after a downshift from rich to poor medium. These findings suggest that protein cost is a transient phenomenon that happens upon an upshift in conditions and that cost is reduced when ribosomes and other cellular systems have increased to their appropriate steady-state level in the new condition.
authors.affiliation: Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Irit
authors.initials: I
authors.lastname: Shachrai
authors.forename: Alon
authors.initials: A
authors.lastname: Zaslaver
authors.forename: Uri
authors.initials: U
authors.lastname: Alon
authors.forename: Erez
authors.initials: E
authors.lastname: Dekel
mesh_terms: D003470:Culture Media / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism*; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D011401:Promoter Regions, Genetic; D011755:Pyrophosphatases / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism
chemical_list: D003470:Culture Media; D029968:Escherichia coli Proteins; D049452:Green Fluorescent Proteins; C027627:guanosine-3',5'-bis(diphosphate) 3'-pyrophosphatase; D011755:Pyrophosphatases; D008025:Ligases; C028812:guanosine 3',5'-polyphosphate synthetases