Figure 2. The Rax C- and N-terminal regions exhibit functional interaction. Full-length (FL) or mutated Rax was assayed for ability to activate expression of a Xenopus rhodopsin gene promoter–luciferase reporter gene. A: Schematic representation of Rax constructs assayed. Numbers indicate amino acid residues. Dotted lines indicate internal deletions. Point mutations are marked by an asterisk (*). B: Alignment of sequences from X. laevis arx and rax OP motifs. C: Luciferase assay results for Rax N-terminal mutations and deletions diagrammed in A. Reporter gene activity is calculated as firefly luciferase activity normalized to Renilla luciferase control and is presented relative to activity of a pCS2-only plasmid control. Values represent the mean of three to nine independent experiments (nine replicates per experiment). Error bars represent standard deviation from the mean. All vector-only and Rax activity values except ΔN39 are statistically significantly different from full-length Rax activity using a corrected (Bonferroni) critical value of p<0.0017 (*p=4.06 × 10⁻⁴⁸, n=81; **p=6.90 × 10⁻⁸, n=27; ***p=7.52 × 10⁻⁶, n=27; ****p=2.13 × 10⁻¹⁴, n=27; *****p=0.00761, n=27). D: Luciferase assay results for Rax constructs containing C-terminal truncations (indicated on the x-axis) and an intact N-terminus (black filled bars), the L38P mutation (gray filled bars), or ΔOP (hatched bars), as shown in Figure 1A or the lower portion of panel A of this figure. All pairwise activity values are statistically significantly different, except where indicated, using a corrected (Bonferroni) critical value of p<0.0017 (^ap=3.34 × 10⁻³⁹, ^bp=4.42 × 10⁻¹⁰, ^cp=3.29 × 10⁻⁸, ^dp=9.50 × 10⁻³⁸, ^ep=1.94 × 10⁻⁸, ^fp=6.53 × 10⁻²⁵, *p=1.87 × 10⁻¹⁷, **p=5.23 × 10⁻¹⁴, ***p=7.12 × 10⁻¹⁹, ****p=8.78 × 10⁻¹¹; in each case, n=27). Abbreviations: HD = homeodomain, NS = not significant, OAR = orthopedia, aristaless, rax, OP = octapeptide domain, PPXY = PPXY motif (putative YAP/TAZ binding sequence), RX = Rx domain. *in constructs containing L38P denotes mutated leucine residues (to proline).