Fig. 7. The conserved N-terminal region of Scr is required for the activation of fkh and CrebA expression. (A) Alignment of the N-termini of insect Scr proteins [Drosophila melanogaster (Dm), Anopheles gambiae (Ag), Tribolium castaneum (Tc) and Bombyx mori (Bm)]. In the region deleted in the ScrSSY mutation (bracket), 12 out of 17 amino acid resides are identical. (B) Expression levels of ectopic wild-type Scr (Scr) and the ScrSSY mutant (SSY) in ventral parasegment 1 (ps 1), compared with the levels of the endogenous Scr protein (wt) in ventral parasegment 2 (ps 2). Error bars: 95% confidence intervals. (C-E) Anterior regions of mid-stage 11 embryos, hybridized with a fkh transcript antisense probe. (C) In wild-type embryos, fkh is activated in ventral parasegment 2. (D) Ectopic wild-type Scr activates fkh transcripts in ventral parasegment 1, the anterior mandibular segment (asterisk) and in the procephalon. (E) Ectopic ScrSSY protein activates fkh transcripts in only a few cells of parasegment 1. (F-H) Mid-stage 11 embryos stained with anti-CrebA antibody. (F) In wild-type embryos, CrebA expression is limited to ventral parasegment 2. (G) Ectopic wild-type Scr activates CrebA in parasegment 1 and the procephalon. (H) Ectopic ScrSSY protein activates CrebA in only a few cells of parasegment 1. (J) Alignment of the N termini of human (Homo sapiens), mouse (Mus musculus), sea urchin (Strongylocentrotus purpuratus) and fly (Drosophila melanogaster) Hox proteins. In all of these proteins, the N terminus conserves an SSYF motif or a subtle variant. Asterisks indicate Hox proteins in which a requirement of the N-terminal region for transcriptional activation in embryos has been demonstrated.