Table 1. The contribution of different steps in gene expression to the variance in protein abundances between genes.

	Variance in protein levels (log10)*	Percent contribution to variance in protein levels
		mRNA(%)	Transcription(%)	RNA degradation(%)	Translation(%)	Protein degradation(%)
Schwanhausser 2nd dataa	0.97	40	34	6	55	5
Measured protein error strategyb	0.34	56	38	18	30	14
Measured translation strategyc	0.61	81	71	10	11	8

^*In this column, the value given for Schwanhausser et al.’s (2011) 2nd data is the variance in their measured protein abundances; the remaining values are our estimate for the variance in true protein levels for different scenarios.

^aEstimates from Schwanhausser et al. (2011) based on the 4,212 genes for which NIH3T3 cell protein and mRNA abundance data are available.

^bOur estimates for the same 4,212 genes studied by Schwanhausser et al. (2011) after correcting the overall scaling of the NIH3T3 cell protein abundance data and taking several sources of molecule specific experimental error into account: stochastic protein error and all mRNA errors.

^cOur estimates for the same 4,212 genes studied by Schwanhausser et al. (2011) derived using measured translation rates from Subtelny et al. (in press).