Fig. 2. Deletion analysis isolates a proximal Xath5 cis-regulatory region. (A) HindIII, DraII and PstI sites were used to delete regions of Xath5 genomic sequence in the pG1X5 construct. All three constructs drove strong transgene expression in the retina. (B) The pG1X5-proximal construct containing sequences from –427 to –1 drove robust retinal expression of the transgene. The pG1X5-TATAA construct containing sequences from –226 to –1 showed no expression. Xath5 sequence from –427 to –226, when fused to the Fos heterologous basal promoter (pG1-cfos-201bp-X5), drove retinal expression, but more weakly. The basal Fos promoter alone (pG1-cfos) did not confer retinal GFP expression. (C) A pG1X5-proximal transgenic embryo (stage 33) shows retinal GFP expression. (D) In situ hybridization of pG1-cfos-201bp-X5 (stage 32) transgenic embryo shows weak GFP expression in the retina.