Expression of the Oct-1 transcription factor and characterization of its interactions with the Bob1 coactivator

The Oct-1 transcription factor regulates a variety of tissue-specific and g eneral housekeeping genes by recruiting specialized coactivators of transcr iption. It acts synergistically with the B-cell-specific coactivator Bob1 ( OCA-B, OBF-1) to stimulate transcription of immunoglobulin genes. To analyz e Octi-1's interactions with Bob1 and other regulatory proteins, we have ov erexpressed and purified different functional domains of the recombinant pr oteins. A version of Oct-1 that encompasses the amino-terminal activation r egion and the POU DNA-binding domain was extensively characterized (Oct Del ta Cl; comprising residues 1-445). Using an in vitro transcription assay, w e demonstrate that this fragment is sufficient and necessary to stimulate t ranscription from an immunoglobulin promoter with Bob1. It also coactivates from the herpes simplex virus ICPO promoter element in the presence of VP1 6. Using a range of spectroscopic and biophysical techniques, we demonstrat e that the activation domains of Oct-1 and Bob1 have little globular struct ure and that they do not physically interact. Thus, their functional synerg y is likely to arise by the co-recruitment of common factors as part of a l arger regulatory assembly. We propose a hypothesis to explain why the activ ation domains of these and other transcription factors of metazoans have li ttle if any intrinsic structure.