Repression of mouse mammary tumor virus transcription by a transcription factor complex. Binding of individual components to separated DNA strands.

Expression of mouse mammary tumor virus in T lymphocytes appears to be required for accession of horizontally transmitted virus to the mammary gland. Further, deletions in the long terminal repeat which relax constraints on viral transcription promote T cell lymphoma. We have identified a polypurine transcriptional repressor element (NRE1) that is deleted from viruses that induce T cell lymphoma. NRE1 binding activity in nuclear extracts proved to be related to a growth inhibitory activity that represses c-myc expression in mature B cells. Mobility shift, DNA foot-printing, and UV cross-linking identified three factors that interacted preferentially with double-stranded NRE1 or the separated single strand