For clinical applications the biological functions of DNA-binding proteins require that they interact with their target binding site with high affinity and specificity. Advances in randomized production and target-oriented selection of engineered artificial DNA binding domains incited a rapidly expanding field of designer transcription factors (TFs). Engineered (TFs) are used in zinc finger nuclease (ZFN) technology that allows targeted genome editing. Zinc-finger binding domains fabricated by modular assembly display an unexpectedly high failure rate having either a lack of activity as ZFNs in human cells or activity at "off-target" binding sites on the human genome causing cell death. To address these shortcomings we created new binding domains using a targeted modification strategy. We produced two Sp1 mutants by exchanging amino acid residues in the alpha-helical region of the transcription factor Sp1. We identified their best target binding sites and searched the NCBI HuRef genome for matches of the 9 base pair consensus binding site of Sp1 and the best binding sites of its mutants. Our research concludes that we can alter the binding preference of existing zinc finger domains without altering its biological funcationalities.