Fig. 7. Identification of lysine 149 as an amino acid which may confer T box specificity. (A) Diagram of Xbra and part of the T box sequences of human, mouse, Xenopus and zebrafish Brachyury. Yellow circles indicate amino acids which contact DNA (Muller and Herrmann, 1997). The sequences are aligned with the equivalent regions of Xenopus VegT and human, mouse, Xenopus and zebrafish Eomesodermin. Note that the K residue in Xbra is replaced by an N in VegT and Eomesodermin. (B) Asterisk (on the left-hand T box) marks the position of K149 on the crystal structure of the Xbra T box bound to DNA (Muller and Herrmann, 1997). (C) Mutation of an asparagine residue in VegT and Eomesodermin to lysine causes those proteins to resemble Xbra in their inducing activities; VegT^NK and Eomesodermin^NK lose the ability to induce Goosecoid and levels of Chordin and Pintallavis are significantly reduced.