ANALYSIS OF HOMEODOMAIN FUNCTION BY STRUCTURE-BASED DESIGN OF A TRANSCRIPTION FACTOR

The homeodomain is a 60-amino acid module which mediates critical prot ein-DNA and protein-protein interactions for a large family of regulat ory proteins. We have used structure-based design to analyze the abili ty of the Oct-1 homeodomain to nucleate an enhancer complex. The Oct-1 protein regulates herpes simplex virus (HSV) gene expression by parti cipating in the formation of a multiprotein complex (C1 complex) which regulates alpha (immediate early) genes, We recently described the de sign of ZFHD1, a chimeric transcription factor containing zinc fingers 1 and 2 of Zif268, a four-residue linker, and the Oct-1 homeodomain. In the presence of alpha-transinduction factor and C1 factor, ZFHD1 ef ficiently nucleates formation of the C1 complex in vitro and specifica lly activates gene expression in vivo. The sequence specificity of ZFH D1 recruits C1 complex formation to an enhancer element which is not e fficiently recognized by Oct-1, ZFHD1 function depends on the recognit ion of the Oct-1 homeodomain surface, These results prove that the Oct -1 homeodomain mediates all the protein-protein interactions that are required to efficiently recruit alpha-transinduction factor and C1 fac tor into a C1 complex. The structure-based design of transcription fac tors should provide valuable tools for dissecting the interactions of DNA-bound domains in other regulatory circuits.