 1. Large-scale surveys in mammalian tissue culture cells suggest that the protein expressed at the median abundance is present at 8,000 to 16,000 molecules per cell and that differences in mRNA expression between genes explain only 10 to 40% of the differences in protein levels. 2. However, we find that these surveys have significantly underestimated protein abundances and the relative importance of transcription. Using individual measurements for 61 housekeeping proteins to rescale whole proteome data from Schwanhauser et al. 2011, we find that the median protein detected is expressed at 170,000 molecules per cell and that our corrected protein abundance estimates show a higher correlation with mRNA abundances than do the uncorrected protein data. 3. In addition, we estimated the impact of further errors in mRNA and protein abundances using direct experimental measurements of these errors. The resulting analysis suggests that mRNA levels explain at least 56% of the differences in protein abundance for the 4,212 genes detected by Schwanhauser et al. 2011, though because one major source of error could not be estimated the true percent contribution should be higher. 4. We also employed a second, independent strategy to determine the contribution of mRNA levels to protein expression. We show that the variance in translation rates directly measured by ribosome profiling is only 9% of that inferred by Schwanhauser et al. 2011 and that the measured and inferred translation rates correlate poorly are 2 equals 0.14. Based on this, our second strategy suggests that mRNA levels explain till the operator 8.4% of the variance in protein levels. 5. We also determined the percent contributions of transcription, RNA degradation, translation and protein degradation to the variance in protein abundances using both of our strategies. While the magnitudes of the two estimates vary, they both suggest that transcription plays a more. This article was authored by Ginny Jessakali, Peter J. Bickel and Mark D. Bighan. We are article.tv, links in the description below.