Variants of the TATA-binding protein can distinguish subsets of RNA polymerase I, II, and III promoters.

Transcription extracts prepared from yeast that are deficient in the TATA-binding protein (TBP or TFIID) are also impaired in specific promoter recognition by all three nuclear RNA polymerases (pol I, II, and III). Specific initiation can be rescued by the addition of purified recombinant TBP, demonstrating that pol I, II, and III all require this factor. A mutation of TBP has been identified that will function with pol I but not with pol II or III. Conversely, another mutation, which inactivates TATA element binding in vitro, will function with pol I and III promoters but is inactive for a pol II promoter. Thus, it is possible to identify TBP variants that will only function on different subsets of all nuclear promoters.