Relative mRNA expression of C-GFP and A-GFP transgenes. Relative mRNA levels among five single-copy clones for eGFP and AID from C-GFP and A-GFP lines were measured by real-time PCR. The data show the mean of three independent experiments. β-Actin mRNA was used to normalize eGFP and AID mRNA levels. The y axis shows mRNA levels relative to clone C6.