Based on the luciferase reporter assay results observed in the −109 to +247 region, we examined this region of the SEPP1 promoter for evidence of response elements that could potentially serve as binding sites for GR or VgEcR, as well as RXR. Two putative GREs were identified using the Transcription Element Search System (Schug & Overton 1997). These response elements are referred to as GRE #1 and GRE #2 and are found at position −87 and −24 of the SEPP1 promoter, respectively. The precise sequences suggest that these sites may not function as classical GREs but appeared to best define half-sites (Nordeen et al. 1990). In addition, a putative retinoid receptor binding site was identified at position −73 of the SEPP1 promoter, and is referred to as a putative RRE. GRE #1 and the RRE are sequential with one another and together could form a potential binding site for VgEcR-RXR. These sites also overlap with a previously characterized HNF-4α binding site in the SEPP1 promoter (Speckmann et al. 2008; Walter et al. 2008).
