TALEN DNA constructs targeting the human CEBPB ORF were constructed using the Golden Gate Talen assembly kit (Addgene. Cambridge, MA USA).30 (link) Targeting sequences were designed using the Cornell University TAL Effector Nucleotide Targeter 2.0 web based software. Golden Gate assembly of the repeat-variable di-residue sequence was performed according to the manufacturer's instructions and the completed TALEN pairs were ligated into the pTAL3 vector. The complete TALEN ORF including the repeat-variable and FokI domains was excised using XhoI and ApaI restriction endonuceases and ligated into the pcDNA3.1(+) vector. LNCaP cells cotransfected with TALEN expression vectors targeting CEBPB were seeded in 96 well dishes, and individual clones were screened for C/EBPβ expression by Western blotting.