Practice question

TBP saddle inserts into minor groove of eight base pair TATA box, using four phenylalanine side chains to intercalate between base steps, causing severe kinking of about eighty degrees toward major groove and slight unwinding. Such dramatic bending partially unwinds DNA, widens minor groove, and creates platform for TFIIA and TFIIB entry. Bending also brings upstream regulatory regions closer to initiation site and introduces strain facilitating promoter melting by TFIIH helicase. Crystallography of TBP-TATA shows twofold symmetric bending creating almost right angle conformation.