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We have applied SPR imaging technique for efficient and precise measurement of the binding of estrogen receptors (ERÂ¿ and ERÃ) with their response elements (EREs) arrayed on chip. Four EREs - one containing a perfect core sequence (GGTCAnnnTGACC), and three containing imperfect cores (i.e., with one base substitution in one of the half-site, GGTCAnnnTGGCC; with one half-site mutant, GGTCAnnnCACGA and a scrambled DNA with both half-site mutant) were involved in this study. ERÂ¿ and ERÃ binding to these sequences at two buffer conditions (higher and lower ionic strength) was measured to determine the salt effects and sequence impact on ER-ERE binding. Distinct binding behaviour of ERÂ¿ and ERÃ has been compared. Conventional SPR experiments were run in parallel to cross check the results from SPR imager and to optimize the assay protocol of the SPR imager. A precise measurement of sequence dependent ER-ERE binding is of significance in determining the rules, by which ERs are recruited by DNA.