The Homeo Domain of a Murine Protein Binds 5′ to Its Own Homeo Box

Nuclear protein extracts from day 12.5 mouse embryos were used to study protein binding to DNA sequences 5′ of the Hox 1.5 homeo box. Embryos of this developmental stage are known to express this gene. DNA binding protein blotting and retardation gel techniques show that murine embryonic nuclear proteins specifically bind a 753-base pair (bp) DNA fragment from the region upstream of the Hox 1.5 homeo box. A fusion protein containing the Hox 1.5 homeo domain constructed in λ gt11 also binds the same 753-bp DNA fragment. Specific binding of the fusion protein to the upstream DNA fragment shows that the homeo box contains the sequences required for specific protein--DNA interactions, and the 753-bp fragment contains a homeo domain binding site. These results support the hypothesis that murine homeo boxes are DNA binding domains of proteins involved in the regulation of embryonic development.