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Summary: Using L929 cells, we quantitated the macroeconomics of protein synthesis and degradation and the microeconomics of producing MHC class I associated peptides from viral translation products. To maintain a content of 2.6 x 109 proteins, each cell's 6 x 106 ribosomes produce 4 x 106 proteins min-1. Each of the cell's 8 x 105 proteasomes degrades 2.5 substrates min-1, creating one MHC class I-peptide complex for each 500-3000 viral translation products degraded. The efficiency of complex formation is similar in dendritic cells and macrophages, which play a critical role in activating T cells in vivo. Proteasomes create antigenic peptides at different efficiencies from two distinct substrate pools: rapidly degraded newly synthesized proteins that clearly represent defective ribosomal products (DRiPs) and a less rapidly degraded pool in which DRiPs may also predominate.

(C) 2003Elsevier, Inc.