The interaction of a c-Jun/Fos related protein factor with the U3 sequences of the mouse mammary tumor virus LTR.

Using polyacrylamide gel mobility shift assay we have detected a nuclear factor (NF-S) in a mouse mammary tumor cell line (GR) that binds to an upstream sequence domain (-766 to -737) near the 5'-end of the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). Antibodies to the products of the Jun and Fos oncogenes interfered with the binding potential of this factor, indicating that the factor shares antigenic determinants with c-Jun/AP-1. In vitro translated c-Jun and c-Fos were also found to bind to the NF-S binding domain consisting of the sequence TGA(A/G)TCA that are known to be recognized by c-Jun/AP-1. Our results raise the possibility that the MMTV-LTR sequence element-766 to -737 by interacting with a Jun/Fos related protein play a role in MMTV transcription and/or the activation of int protooncogenes that are associated with murine mammary tumorigenesis.