Purification and properties of the Drosophila zen protein.

The zen protein is encoded by the zerknullt gene required for normal early development in Drosophila. Like many regulatory proteins of this type, zen contains a 60 amino acid homeobox sequence. We have purified the zen protein and studied its solution behavior and its interaction with DNA. The zen protein exists as a monomer in solution with a molecular weight of about 40,000. It binds specifically to a site about 900 bases upstream from the zen gene. Within this binding site DNase protection experiments indicate that binding is confined to two regions approximately 11 and 14 bases in length that are separated by about 30 base pairs. The protein concentration dependence of the binding curve suggests that protein binding is non cooperative.