mTORC1 is known to stimulate protein synthesis; now, it is shown to also promote the synthesis of proteasomes, which degrade proteins into the amino acids needed to create new proteins. Cells continuously monitor opportunities for growth. When conditions are favourable, the mTOR signalling pathway is activated, stimulating the conversion of nutrients such as amino acids into cellular building blocks such as proteins. Nonetheless, Brendan Manning and colleagues report that the very same signalling pathway promotes protein degradation: downstream of mTORC1 the transcription factor NRF1 becomes active, inducing the expression of genes that encode subunits of the proteasome, increasing the levels of active proteasome, and stimulating protein turnover. But what is the point of simultaneously promoting protein synthesis and protein degradation? The authors find that the amino acids generated by the mTOR pathway through protein degradation facilitate the synthesis of new proteins. Eukaryotic cells coordinately control anabolic and catabolic processes to maintain cell and tissue homeostasis. Mechanistic target of rapamycin complex 1 (mTORC1) promotes nutrient-consuming anabolic processes, such as protein synthesis1. Here we show that as well as increasing protein synthesis, mTORC1 activation in mouse and human cells also promotes an increased capacity for protein degradation. Cells with activated mTORC1 exhibited elevated levels of intact and active proteasomes through a global increase in the expression of genes encoding proteasome subunits. The increase in proteasome gene expression, cellular proteasome content, and rates of protein turnover downstream of mTORC1 were all dependent on induction of the transcription factor nuclear factor erythroid-derived 2-related factor 1 (NRF1; also known as NFE2L1). Genetic activation of mTORC1 through loss of the tuberous sclerosis complex tumour suppressors, TSC1 or TSC2, or physiological activation of mTORC1 in response to growth factors or feeding resulted in increased NRF1 expression in cells and tissues. We find that this NRF1-dependent elevation in proteasome levels serves to increase the intracellular pool of amino acids, which thereby influences rates of new protein synthesis. Therefore, mTORC1 signalling increases the efficiency of proteasome-mediated protein degradation for both quality control and as a mechanism to supply substrate for sustained protein synthesis.