| Activating signal cointegrator 1 ( ASC 1 ) harbors an autonomous transactivation domain that contains a putative zinc finger motif which provides binding sites for basal transcription factors TBP and TFIIA , transcription integrators steroid receptor coactivator 1 ( SRC 1 ) and CBP p 300 , and nuclear receptors , as demonstrated by the glutathione S transferase pull down assays and the yeast two hybrid tests . ^^^ Activating signal cointegrator 1 ( ASC 1 ) harbors an autonomous transactivation domain that contains a putative zinc finger motif which provides binding sites for basal transcription factors TBP and TFIIA , transcription integrators steroid receptor coactivator 1 ( SRC 1 ) and CBP p 300 , and nuclear receptors , as demonstrated by the glutathione S transferase pull down assays and the yeast two hybrid tests . ^^^ Nonetheless , ASC 1 appears to require the AF 2 dependent factors to function ( i . e . , CBP p 300 and SRC 1 ) , as suggested by the ability of ASC 1 to coactivate nuclear receptors , either alone or in cooperation with SRC 1 and p 300 , as well as its inability to coactivate a mutant receptor lacking the AF 2 core domain . ^^^ By using indirect immunofluorescence , we further show that ASC 1 , a nuclear protein , is localized to the cytoplasm under conditions of serum deprivation but is retained in the nucleus when it is serum starved in the presence of ligand or coexpressed CBP or SRC 1 . ^^^ These results suggest that ASC 1 is a novel coactivator molecule of nuclear receptors which functions in conjunction with CBP p 300 and SRC 1 and may play an important role in establishing distinct coactivator complexes under different cellular conditions . . ^^^ |