TBP and TFIIB are both required to induce slipping on a bubble
template. A, leaving either TBP or TFIIB out of transcription
reactions eliminates transcript slippage. Reactions were performed on the
wild-type template in the presence of GTP (productive 12-nt product is
indicated with an asterisk). The factors were omitted from reactions
as indicated. A darker exposure of the same gel is shown to the
right. B, TBP and TFIIB function together to cause slipping.
Reactions were performed on the wild-type template in the presence of GTP,
with the factors added in the combinations indicated. C, higher
concentrations of either TBP or TFIIB do not force transcript slippage. TBP,
TFIIB, and both factors together were added to reactions at 1×,
3×, and 10× the standard concentrations. Transcription occurred on
the wild-type template in the absence of GTP.