| The ability of this cis acting RAR RXR binding element to activate transcription in response to RA also depended on downstream sequences where an octamer transcription factor 1 ( Oct 1 ) site and a nuclear factor of activated T cells ( NFATc ) site between this element and the transcriptional start , as well as a cyclic AMP response element binding factor ( CREB ) site between the transcriptional start and first exon of the blr 1 gene , were necessary . ^^^ This cis acting element approximately 1 kb upstream of the transcriptional start consists of two GT boxes that bind RAR and RXR in a nuclear protein complex that also contains Oct 1 , NFATc 3 , and CREB 2 bound to their cognate downstream consensus binding sites . . ^^^ A transcription factor transcription factor binding array analysis of nuclear lysate from RA treated cells indicated several prominent RARalpha binding partners ; among these , Oct 1 , NFATc 3 , and CREB 2 were identified by competition EMSA and supershift and chromatin immunoprecipitation assays as components of the complex . ^^^ |