Zinc finger nucleases (ZFNs) are associated with cell death and apoptosis by 
binding at countless undesired locations. This cytotoxicity is associated with 
the binding ability of engineered zinc finger domains to bind dissimilar DNA 
sequences with high affinity. In general, binding preferences of transcription 
factors are associated with significant degenerated diversity and complexity 
which convolutes the design and engineering of precise DNA binding domains. 
Evolutionary success of natural zinc finger proteins, however, evinces that 
nature created specific evolutionary traits and strategies, such as modularity 
and rank-specific recognition to cope with binding complexity that are critical 
for creating clinical viable tools to precisely modify the human genome. Our 
findings indicate preservation of general modularity and significant alteration 
of the rank-specific binding preferences of the three-finger binding domain of 
transcription factor SP1 when exchanging amino acids in the 2nd finger.