Alkylation interference identifies essential DNA contacts for sequence-specific binding of the eukaryotic transcription factor C/EBP.

Transcriptional regulators containing a "leucine zipper" and a flanking basic domain belong to a recently identified class of DNA-binding proteins. We have mapped the essential DNA contacts of one member of this group, the eukaryotic transcription factor C/EBP. Methylation and ethylation interference experiments detected major groove contacts over a full turn of the DNA helix on both an asymmetric and a symmetric C/EBP binding site. The contacts essential for C/EBP binding have two-fold symmetry yet differ significantly from the contacts of other dimeric DNA-binding proteins, including those bearing helix-turn-helix motifs and the type I restriction endonuclease EcoRI.