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pubmed:abstractText |
Murine F9 embryonal carcinoma (F9 EC) stem cells have an E1a-like transcription activity that is down-regulated as these cells differentiate to parietal endoderm. For the adenovirus E2A promoter, this activity requires at least two sequence-specific transcription factors, one that binds the cyclic AMP-responsive element (CRE) and the other, DRTF1, the DNA-binding activity of which is down-regulated as F9 EC cells differentiate. Here we report the characterization of several binding activities in F9 EC cell extracts, referred to as DRTF 1a, 1b and 1c, that recognize the DRTF1 cis-regulatory sequence (-70 to -50 region). These activities can be chromatographically separated but are not distinguishable by DNA sequence specificity. Activity 1a is a detergent-sensitive complex in which DNA binding is regulated by phosphorylation. In contrast, activities 1b and 1c are unaffected by these treatments but exist as multicomponent protein complexes even before DNA binding. Two sets of DNA-binding polypeptides, p50DR and p30DR, affinity purified from F9 EC cell extracts produce complexes 1b and 1c. Both polypeptides appear to be present in the same DNA-bound protein complex and both directly contact DNA. These affinity-purified polypeptides activate transcription in vitro in a binding-site-dependent manner. These data indicate the in F9 EC stem cells, multicomponent differentiation-regulated transcription factors contribute to the cellular E1a-like activity.
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