Purified glucocorticoid receptor-hormone complex from rat liver cytosol binds specifically to cloned mouse mammary tumor virus long terminal repeats in vitro.

Purified glucocorticoid hormone-receptor complex (HRC) from rat liver binds to specific DNA sequences contained in cloned mouse mammary tumor virus (MMTV)DNA. The binding site of the hormone-receptor complex is located in the long terminal repeat (LTR) of MMTV DNA as shown by filter binding studies with labeled restriction fragments and by visualization of DNA-receptor complexes with the electron microscope. The DNAs from cloned MMTV lacking the LTR sequences were neither retained on nitrocellulose filters nor bound specifically to HRCs examined in the electron microscope. The HRC also failed to bind to restriction fragments from pBR322 and phage lambda. Specific binding of the HRC to LTR sequences is dependent upon occupancy of the receptor by a glucocorticoid. Previous work has demonstrated that the MMTV transcription is initiated within the LTR; additionally, MMTV transcription is known to be regulated by glucocorticoids. Our present results therefore support the hypothesis that HRC regulates hormone-induced transcription by binding to specific DNA sequences near the MMTV transcription start site.