The concentration of the cognate protein in the cell is governed by both protein synthesis (driven by transcription) and protein degrdation (influenced by many factors). The expressed gene gives the potential for a protein to be expressed but can't be directly correlated in many cases. See: "Chen, G, Gharib, T G, Huang, C C, et al. Discordant protein and mRNA expression in lung adenocarcinomas, Mol Cell Proteomics, 1, 304-313 (2002)"; "4. Mehra, A, Lee KH, and Hatzimanikatis V. Insights into the relation between mRNA and protein expression patterns: I. Theoretical considerations. Biotechnol Bioeng, 2003. 84 (7) 822-33."; "7. Anderson, L and Seilhamer, J. A comparison of selected mRNA and protein abundances in human liver, Electrophoresis, 18 (3-4), 533-7 (1997)." ; "Doherty MK and Beynon RJ. (2006): Protein dynamics on the scale of the proteome, Exp. Rev. Proteomics, 3 (1), 97-110."