The targeted FP integration leads to endogenous expression of the corresponding fusion proteins.

<p>Wild type (WT) and ZFN modified (STAT1-GFP/RFP-STAT3) cell lysates were analyzed by Western blot with and without STAT1/STAT3 activation using antibodies recognizing epitopes on FP tags and phosphorylated and total STATs. α-Tubulin or total STAT3 levels were analyzed as loading controls. The molecular weights of unmodified and FP-tagged STATs are around 90 and 120 kDa, respectively. At least one copy was tagged and at least one copy was untagged for each STAT. In the case of STAT1, expression of only its major isoform STAT1α lead to STAT1-GFP fusion protein production while all STAT3 isoforms were tagged if expressed off the gene copy with the FP insert.