PT - JOURNAL ARTICLE AU - Eyal Metzl-Raz AU - Moshe Kafri AU - Gilad Yaakov AU - Ilya Soifer AU - Yonat Gurvich AU - Naama Barkai TI - Principles of cellular resource allocation revealed by condition-dependent proteome profiling AID - 10.1101/124370 DP - 2017 Jan 01 TA - bioRxiv PG - 124370 4099 - http://biorxiv.org/content/early/2017/04/05/124370.short 4100 - http://biorxiv.org/content/early/2017/04/05/124370.full AB - Growing cells devote much of their resources to producing ribosomes. Translation of ribosomal proteins competes with the production of other proteins, suggesting that cells optimize growth by producing the precise number of ribosomes required for meeting translation demands. Alternatively, maintaining a pool of ready-to-use ribosomes could facilitate a response to fluctuating conditions. To examine how cells balance their ribosomal content, we used proteome profiling. Differences in ribosomal proteins levels in cells growing at different rates precisely accounted for the estimated differences in translation rates. However, in all conditions, 8% of the proteome coded for extra ribosomal proteins, produced in addition to the growth-rate dependent fraction. This pool of extra ribosomal proteins, consisting of ∼20% of the expressed ribosomes in fast growing cells and the majority of ribosomes in slow-growing ones, was employed upon unexpected increase in translation demands, for example during nutrient upshift and when forcing excess protein production. Cells therefore tune their ribosome content and activity to balance the opposing requirements of rapid growth with rapid response to fluctuating conditions.