BASAL COMPONENTS OF THE TRANSCRIPTION APPARATUS (RNA-POLYMERASE-II, TATA-BINDING PROTEIN) CONTAIN ACTIVATION DOMAINS - IS THE REPETITIVE C-TERMINAL DOMAIN (CTD) OF RNA-POLYMERASE-II A PORTABLE ENHANCER DOMAIN

Regions rich in serine, threonine, and proline residues can be found i n transcriptional activation domains, as well as in the N-terminal par ts of mammalian TATA-binding proteins, where they are interrupted by p olyglutamine stretches. Likewise, the C-terminal domain of the largest subunit of RNA polymerase II contains multiple repeats of the consens us heptapeptide sequence YSPTSPS. To test directly for possible activa tion functions, we fused the GAL4 DNA-binding domain to the N-terminal domain of human TBP or subdomains of it, and to the C-terminal domain (CTD) of mouse RNA polymerase II or synthetic polymers of a CTD conse nsus repeat. We found that these chimeric proteins were able to activa te transcription when bound to a GAL4 site in front of the TATA box, a function characteristic of transcription factors. However, while subd omains of TBP functioned only from a position close to the TATA box (' 'promoter'' position), multiple repeats of the CTD consensus sequence were also able to mediate transcriptional activation from a remote ('' enhancer'') position. Our findings suggest that a region of TBP that i s unique to mammals functionally cooperates with ''proximal'' activati on domains of promoter-bound transcription factors. They also imply th at the C-terminal domain of RNA polymerase II includes a function that is otherwise confined to remote activation domains of enhancer-bound transcription factors. We suggest that the CTD of RNA polymerase II co ntains a ''portable'' remote activation domain that may also facilitat e chromatin opening within the transcription unit. (C) 1994 Wiley-Liss , Inc.