Characterization of the factor E1BF from a rat hepatoma that modulates ribosomal RNA gene transcription and its relationship to the human Ku autoantigen.

We have purified the DNA binding protein E1BF (Enhancer 1 Binding Factor) from the nuclei of Morris hepatoma 3924A. This protein, which consists of two polypeptides of 72 kDa and 85 kDa, binds to several DNA sequences involved in the regulation of rDNA transcription. UV-crosslinking studies show that interaction of the protein with DNA is primarily through the 72 kDa polypeptide. Purified E1BF can also modulate pol I-directed transcription in a cell-free systems derived from rat and mouse. E1BF is related to the human autoantigen Ku as demonstrated by immunological cross-reactivity with monoclonal antibodies directed against Ku p70 in Western blot and gel mobility shift assays.