Mark Biggin of the Lawrence Berkeley National Laboratory contacted us, noting that our mass-spectrometry-based protein copy number estimates are lower than several literature-based values. We therefore re-analysed the scripts used for data processing, and found a scaling error that occurred during the conversion of normalized protein intensity values into absolute copy number estimates. As described in the original Article, slope and offset for scaling were calculated by linear regression based on an in-solution digest with spiked-in proteins of known concentrations. We erroneously used the slope and the offset from an unrelated experiment to scale protein levels, resulting in a systematic underestimation of protein levels and derived translation rate constants. We apologize for this error and any confusion it may have caused.

When the error was corrected, the median levels of detected proteins increased about threefold and the ratio of average protein to messenger RNA increased from 900 to 2,800. The median and apparent maximum translation rate constants increased from 40 to 140 and from 180 to 1,000 proteins per mRNA per hour, respectively. Consequently, the estimated maximum translation rate constant in sea urchin embryos at 15 uC (140 proteins per mRNA per hour) is lower than our corrected prediction for mouse fibroblasts (1,000 proteins per mRNA per hour). All our conclusions about global gene expression control (correlations between mRNA and protein levels and half-lives, predominant control of protein abundance at the level of translation, functional properties of genes with specific half-life