Estrogen receptor selectively binds the "coding strand" of an estrogen responsive element.

Area of Science:

• Molecular Biology
• Genetics
• Endocrinology

Background:

• Estrogen stimulates prolactin gene transcription via estrogen-responsive elements (ERE).
• The estrogen receptor (ER) complex binds to EREs as an initial step in transcriptional activation.

Purpose of the Study:

• To investigate the binding mechanism of the estrogen receptor to the ERE of the rat prolactin gene.
• To elucidate the role of DNA strand separation in estrogen receptor binding.

Main Methods:

• Gel mobility assay was used to examine the binding of purified estrogen receptor to a specific DNA fragment containing the ERE.
• Analysis of binding affinities to double-stranded and single-stranded DNA fragments.

Main Results:

• Estrogen receptor exhibited specific high-affinity binding to the coding strand of the ERE, but not the noncoding strand.
• Binding affinity to the coding strand was significantly higher (60-fold) than to the double-stranded ERE.
• The receptor bound 1000-fold more strongly to the single-stranded coding strand than to a non-specific double-stranded DNA.

Conclusions:

• Estrogen receptor binding to the ERE may involve initial binding to the double-stranded ERE, followed by strand separation and tighter binding to the folded coding strand.
• This specific coding strand-receptor complex formation is proposed as a critical step in estrogen-mediated transcriptional activation of the prolactin gene.