ACTIVATION FUNCTIONS OF TRANSCRIPTION FACTOR SP1 AT U2 SNRNA AND TATABOX PROMOTERS

To localize regions in the human transcription factor Sp1, which are i nvolved in activating transcription of the U2 snRNA gene promoter and of a TATA box gene promoter, the activation potentials of GAL4/Sp1 chi meras were analyzed in mammalian cells. In vitro mutagenesis analysis of Spl showed that mutation of a hydrophobic amino acid residue in glu tamine-rich activation domain A impairs stimulation of transcription f rom the TATA box promoter, but not from the U2 promoter. Furthermore, we found that similar parts of Spl are involved in synergistic activat ion of transcription together with the SV40 enhancer and with an enhan cer which binds a single type of transcription factor. This suggests t hat the activating mechanism of Spl is the same with both enhancers, I nterestingly, we found that the glutamine-rich domains A and B, that s timulate transcription from the TATA box promoter were not sufficient for U2 gene activation, Stimulation of U2 transcription required amino acid residues 231-485 of Spl, which contain the glutamine-rich domain B and a serine/threonine-rich part. Since overlapping, but non-identi cal parts of Spl are required for activation of the two promoter types , we conclude that Spl activates the U2 snRNA and TATA box promoters b y different mechanisms.