NUCLEOSOME-MEDIATED DISRUPTION OF TRANSCRIPTION FACTOR-CHROMATIN INITIATION-COMPLEXES AT THE MOUSE MAMMARY-TUMOR VIRUS LONG TERMINAL REPEAT IN-VIVO

Glucocorticoid induction of mouse mammary tumor virus (MMTV) is short lived, returning to base levels within 24 h despite the continued presence of hormone. MMTV DNA sequences assembled as chromatin require hormone for binding by nuclear factor 1 (NF1) and octamer proteins (OCT). However, in the same cells, NF1 and OCT factors are bound to transiently introduced DNA in the absence of hormone. In contrast, recruitment of the TATA-binding protein and a novel DNA-binding protein, which we have designated F(DT), for factor downstream of the TATA-binding protein, is hormone dependent for both stable and transient templates. Furthermore, transient DNA templates, but not nucleosomal templates, retain these transcription factors over the course of 24 h. This finding suggests that MMTV chromatin structure contributes to activation and cessation of transcription in vivo.