Glucocorticoid responsiveness of the transcriptional enhancer of Moloney Murine Sarcoma Virus

The long terminal repeat of Moloney Murine Sarcoma Virus (MoMSV) contains an imperfect direct repeat that serves as a strong transcriptional enhancer. The strength of the MoMSV enhancer is strongly dependent on the presence of glucocorticoid hormone. Mapping studies in combination with DNAase I footprinting experiments define the presence of glucocorticoid regulatory elements at the promoter-proximal ends of each enhancer repeat. These elements behave like inducible enhancers: their regulatory activity is independent of position and orientation when they are linked in cis to a heterologous promoter. These data demonstrate the modular nature of the MoMSV enhancer and identify the glucocorticoid receptor as one of the trans-acting factors that interact with the MoMSV enhancer and mediate its transcriptional activity.