Figure 1.

The construction of the floxed AR fragment. The PKI vector is modified from the pBluescript plasmid. It contains a T7 promoter at the 3′ end, a T3 promoter at the 5′ end, two multiple cloning sites (MCS), two lox sites (▹), a positive Neo selective marker (PKG-Neo^r), and a negative thymidine kinase selective marker (MCT-TK). For the cloning, the XhoI site at the 5′ end MCS was first destroyed. A 3-kb intron 2 fragment was introduced into the 3′ EcoR1 cloning site (R1), followed by a fragment containing intron 1, exon 2, and a small fragment of intron 2 sequences into 5′ XbaI site (X). A lox sequence plus an artificial KpnI site were finally inserted into the XhoI site shortly 5′ to the beginning of exon 2. The constructed plasmid was linearized by NotI before being electroporated into ES cells.