Amino acid substitutions in the SP1 zinc finger domain alter the DNA binding affinity to cognate SP1 target site

Non conserved amino acids, which are located in the postulated α-helical region of the third zinc finger in human transcription factor SP1, have been replaced by amino acids, which occur at the analogous zinc finger position in human protein Kox 15. This helical domain was mutated from SP D HL SK H to S S HL IQ H (SP1-M3). Aspartic acid (D), serine (S) and lysine (K) were substituted by serine (S), isoleucine (I) and glutamine (Q). The DNA binding of the mutated SP1-M3 protein to the SP 1 cognate target site GGG GCG GGG was significantly impaired, indicating that the amino acids, aspartic acid, serine and lysine play a pivotal role in DNA recognition. The mutated SP1 finger cannot imitate the function of the wild type SP1 finger in interacting with the cognate SP1 target site. This structure-function analysis indicates that the third SP1 zinc finger participates in sequence-specific DNA recognition. Thus, the affinity of zinc finger domains can be altered by substituting a limited number of amino acids. This observation is consistent with the notion that zinc finger domains are positioned in the major groove of the DNA and wrap around the DNA. Structure-function analysis of this kind might lead to the description of a zinc finger specific recognition code.