Interaction of the TGGCA-binding protein with upstream sequences is required for efficient transcription of mouse mammary tumor virus.

A high-affinity binding site for the TGGCA-binding protein, also known as nuclear factor I, has previously been shown to reside within the mouse mammary tumor virus (MMTV) long terminal repeat. We have introduced mutations into this binding site to test the importance of this ubiquitous nuclear protein in MMTV transcription. Mutations which abolish the binding of the TGGCA protein in vitro are shown to impair strongly glucocorticoid-induced transcription from this promoter in vivo. These data demonstrate that the TGGCA-binding protein is a multifunctional DNA-binding protein, capable of serving a transcriptional role in the case of MMTV, in addition to its known involvement in the replication of adenovirus.