RECRUITING TATA-BINDING PROTEIN TO A PROMOTER - TRANSCRIPTIONAL ACTIVATION WITHOUT AN UPSTREAM ACTIVATOR

The binding of TATA-binding protein (TBP) to the TATA element is the f irst step in the initiation of RNA polymerase II transcription from ma ny promoters in vitro. It has been proposed that upstream activator pr oteins stimulate transcription by recruiting TBP to the promoter, thus facilitating the assembly of a transcription complex. However, the ro le of activator proteins acting at this step to stimulate transcriptio n in vivo remains largely speculative, To test whether recruitment of TBP to the promoter is sufficient for transcriptional activation in vi vo, we constructed a hybrid protein containing TBP of the yeast Saccha romgces cerevisiae fused to the DNA-binding domain of GAL4. Our result s show that TBP recruited by the GAL4 DNA-binding domain to promoters bearing a GAL4-binding site can interact with the TATA element and dir ect high levels of transcription. This finding indicates that binding of TBP to promoters in S. cerevisiae is a major rate-limiting step acc elerated by upstream activator proteins.