A NEW DNA-BINDING MOTIF IN THE SKN-1 BINDING DOMAIN DNA COMPLEX

The DNA-binding domain of Skn-1, a developmental transcription factor that specifies mesoderm in C. elegans, is shown by X-ray crystallograp hy to have a novel fold in which a compact, monomeric, four-helix unit organizes two DNA-contact elements. At the C-terminus, a helix extend s from the domain to occupy the major groove of DNA in a manner simila r to bZip proteins. Skn-1, however, lacks the leucine zipper found in all bZips. Additional contacts with the DNA are made by a short basic segment at the N-terminus of the domain, reminiscent of the 'homeodoma in arm'.