The transcription factors Sp1 and Oct-1 interact physically to regulate human U2 snRNA gene expression

The expression of human small nuclear U2 RNA genes is controlled by the proximal sequence element (PSE), which determines the start site of transcription, and a distal sequence element (DSE), The DSE contains an octamer element and three Spl binding sites, The octamer, like the PSE, is essential for U2 transcription, The Spl sites contribute to full promoter activity by distance-dependent cooperative interactions with the transcription factors Spl and Oct-1, Here we show that purified recombinant Spl and Oct-1 bind cooperatively to the DSE and that they physically interact in vitro, Furthermore, we show that Spl and Oct-1 interact in vivo using a yeast two-hybrid system, The domain of Spl which interacts with Oct-1 is confined to the region necessary for transcriptional stimulation of U2 RNA transcription, This region contains the glutamine-rich activation domain B and a serine/threonine-rich part. The results demonstrate that Spl, in addition to binding to a number of other factors, also interacts directly with transcription factor Oct-1.