Fig. 7. XGrhl1 modulates XK81A1 keratin promoter activity specifically. (A) A region upstream of the XK81A1 transcriptional start site (red) has significant homology with a Drosophila GRH consensus sequence. Green type indicates a previously defined XAP-2-binding sequence. Mutation of a 4 bp motif (blue line; M2) blocks XGRHL1 binding. (B) Loss of the -200 XGRHL1-binding motif results in a significant defect in XK81A1 promoter activity. Whole embryo reporter assays were performed using XK81A1 keratin promoter sequences linked in cis to the firefly luciferase gene. All values were standardized to the full-length wild-type promoter sequence (arbitrary value of 1). KP487, previously defined XK81A1 promoter; M157E, deletion of previously defined AP-2-binding motif; M2, mutation of the putative XGRHL1-binding site; M2M157E, AP-2/XGRHL1 double mutant; -113KP487, deletion of promoter region with epidermal-specific activity. (C) Expression of 227XGrhl1 blocks XK81A1 promoter activity. The full-length XK81A1 luciferase reporter construct (KP487), a XK81A1 reporter construct in which the XGRHL1-binding site was mutated (M2), or a luciferase only control (pGL3) was co-injected into animal pole blastomeres at the four-cell stage with or without 227XGrhl1-encoding transcripts. Luciferase reporter assays were performed as described in B. All values were standardized with respect to the full-length wild-type promoter sequence (arbitrary value of 1).