Relationship between mRNA and protein expression. Correlation between mRNA and protein expression in Iec-6 cells for CYP2B2 (A), CYP3A1 (B), CYP3A2 (C), CYP3A9 (D), ABCB1a/b (E), ABCC1 (F), and ABCC2 (G). A best fit to the data was observed by linear regression for all CYPs and transporters with the exception of CYP3A1, which was best described by linear regression.