NMR structure of transcription factor Sp1 DNA binding domain

To understand the DNA recognition mechanism of zinc finger motifs of transcription factor Sp1, we have determined the solution structure of DNA-binding domain of the Sp1 by solution NMR techniques. The DNA-binding domain of Sp1 consists of three Cys(2)His(2)-type zinc finger motifs. They have typical betabetaalpha zinc finger folds and relatively random orientations. From DNA-binding analysis performed by NMR and comparison between structures determined here and previously reported structures of other zinc fingers, it was assumed that DNA recognition modes of fingers 2 and 3 would be similar to those of fingers of Zif268, in which each finger recognizes four base pairs strictly by using residues at positions -1, 2, 3, and 6 of the recognition helix. On the contrary, finger 1 can use only two residues for DNA recognition, Lys550 and His553 at positions -1 and 3 of the helix, and has more relaxed sequence and site specificity than other Cys(2)His(2) zinc fingers. It is proposed that this relaxed property of finger 1 allows transcription factor Sp1 to bind various DNA sequences with high affinity.