ABSTRACT
Initiation of RNA polymerase II-directed transcription is mediated by DNA sequence specific activator proteins interacting with components of the basal transcription machinery. NFI/CTF is a family of such binding proteins which have been shown to stimulate transcription via proline-rich activation domains. In order to identify residues crucial for its activator function, a pool of CTF1 mutants was cloned and fused to the bacterial repressor LexA. Transcriptional activation of these constructs was monitored in a Saccharomyces cerevisiae reporter assay. Our studies reveal the existence of a core domain in CTF1 between residues 463 and 508 essential for transcriptional activation functions. It contains the sequence motif SPTSPSYSP, which is strongly related to the heptapeptide repeat YSPTSPS present in the carboxyterminal domain (CTD) of RNA polymerase II. Removal of the entire CTD related motif, as well as substitution of key amino acids therein, abolish CTF1 mediated transcriptional activation.
