FIGURE 9-1 Contributions of the major processes that regulate protein concentrations. The concentration of a protein is controlled by regulation of the frequency with which the mRNA encoding the protein is synthesized (gene transcription), the rate at which that mRNA is degraded, the rate at which that mRNA is translated into protein, and the rate at which that protein is degraded. The relative contributions of these four rates to determining the concentrations of thousands of proteins in cultured mouse fibroblasts were determined by mass spectrometry to measure protein concentrations (see Chapter 3), mRNA sequencing (RNA-seq) to measure mRNA levels (see Chapter 6), protection of mRNA from ribonuclease digestion by associated ribosomes (ribosome footprinting) to estimate translation rates, stable isotope labeling to determine degradation rates, and statistical analysis of the data to correct for inherent biases and errors in these methods.

[Data from J. J. Li and M. D. Biggin, 2014, Science 347:1066.]