Fig. 1. Structure of the Bts1 protein. (A) Zinc finger domains of the 11 zebrafish Btd/Sp-family members (Bts proteins) isolated, aligned with the corresponding domains of Drosophila Btd (Wimmer et al., 1993) and mouse Sp1 (Kadonaga et al., 1987). Positions of the primers used in the degenerate PCR reaction are indicated (arrows). Each zinc finger has the structure 3x(C2H2) (red boxes highlight Cys and His residues) and is preceded by a ‘Btd box’ (boxed in black for Btd, mouse Sp1 and Bts1, not indicated for others). The Cys doublet mutated in the negative control-construct Bts1^C->T (see Fig. 5) is boxed in blue. The expression profile of each bts gene at the tail bud stage is summarized in the right column. jct, junction; gl, gland; ND, not determined; NT, neural tube; olf, olfactory placodes; TB, tail bud; ves, vesicle. (B) Sequence of the Bts1 protein. The zinc-finger domains are in red and the Btd-box is boxed in black. S/T and Q-rich, potential transcriptional activation domains are, respectively, in green and blue. The N-terminal domain resembling that of Sp1, Sp2, Sp4 and Sp5 is underlined. (C) Structural alignment of Bts1 and other Btd/Sp proteins (Kadonaga et al., 1987; Hagen et al., 1992; Wimmer et al., 1993; Wimmer et al., 1996; Supp et al., 1996; Harrison et al., 2000). Percentages of similarity between Bts1 and other proteins are given for the zinc finger/Btd box (red/black). Q-rich domains are blue (the Q domain of Bts1 only resembles that of Btd (dark blue) but does not align with others (light blue)). S/T-rich domains are green and the N-terminal domain grey. The transcriptional activation domains identified in Sp1, Sp3 and Sp4 are labelled A-D.