ESTROGEN-RECEPTOR BINDING TO DNA - AFFINITY FOR NONPALINDROMIC ELEMENTS FROM THE RAT PROLACTIN GENE

The estrogen receptor (ER) binds with high affinity to the nonclassica l estrogen response elements (ERE) found in the rat prolactin gene. Th ere are two putative EREs in this gene; at -1582 and -1722 upstream of the transcriptional start site. We used DNA binding assays based on t he immunoprecipitation of receptor with bound DNA to quantitate the bi nding of ER to these two elements, ER bound each element with signific antly higher affinity than it bound to nonspecific DNA, but with 10-10 0-fold less affinity than that for the classical ERE sequence derived from the vitellogenin A2 gene. These comparisons rank the prolactin ge ne sequences as weak EREs. We also observed a 1:1 ratio of ER to ERE i n the bound complexes, indicating that these high-affinity interaction s were not dependent upon an ER homodimer. These data support the role of these sequences in mediating estrogen regulation of the prolactin gene.