Determinants of T box protein specificity

Members of the T box family of transcription factors play important roles i n early development. Different members of the family exert different effect s and here we show that much of the specificity of the Xenopus T box protei ns Xbra, VegT and Eomesodermin resides in the DNA-binding domain, or T box. Binding site selection experiments show that the three proteins bind the s ame core sequence, but they select paired sites that differ in their orient ation and spacing. Lysine 149 of Xbra is conserved in all Brachyury homolog ues, while the corresponding amino acid in VegT and Eomesodermin is asparag ine. Mutation of this amino acid to lysine changes the inductive abilities of VegT and Eomesodermin to resemble that of Xbra.