Animalia Animals Article Base Sequence DNA binding protein DNA fragment DNA sequence DNA-Binding Proteins Drosophila Proteins Drosophila melanogaster Drosophila protein Drosophila virilis Embryo, Nonmammalian Enhancer Elements, Genetic Gene Expression Regulation Homeodomain Proteins Hox protein Molecular Sequence Data Protein Binding Sequence Alignment Transcription Factors Ubx protein, Drosophila animal animal cell animal embryo binding affinity binding site chromatin immunoprecipitation controlled study embryo