TRANSCRIPTIONAL ACTIVATION OF NFI CTF1 DEPENDS ON A SEQUENCE MOTIF STRONGLY RELATED TO THE CARBOXYTERMINAL DOMAIN OF RNA-POLYMERASE-II/

Initiation of RNA polymerase II-directed transcription is mediated by DNA sequence specific activator proteins interacting with components o f the basal transcription machinery. NFI/CTF is a family of such bindi ng proteins which have been shown to stimulate transcription via proli ne-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 con structs was monitored in a Saccharomyces cerevisiae reporter assay. Ou r studies reveal the existence of a core domain in CTF1 between residu es 463 and 508 essential for transcriptional activation functions. It contains the sequence motif SPTSPSYSP, which is strongly related to th e heptapeptide repeat YSPTSPS present in the carboxyterminal domain (C TD) 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.