Question

During transcription holoenzyme RNA polymerase binds to a DNA sequence and the DNA assumes a saddle like structure at that point. What is that sequence called?

• A. CAAT box
• B. GGTT box
• C. AAAT box
• D. TATA box

Answer 1

Answer: (D)

TATA box

Promoters of RNA polymerase II have three conserved sequences which are present between 25 bp to 100 bp upstream the start site. TATA box is located 20 bp upstream the start site and has a consensus sequence as “TATAA/TAA/T”. CAAT box is located 70-80 bp upstream the start site and has consensus sequence as “GGT/ACAATCT”. GC box (GGGC GG) is present in single or multiple copies at 60 to 100 bp upstream the start site. Transcription begins with binding of TATA-binding protein (TBP) to the TATA box. The TFIIB, which is bound to TBP, also binds to DNA on either side of TBP. TBP insert amino acid side-chains between base pairs causing DNA distortion thereby partially unwinding the helix and producing kink. TBP is rich in positively charged lysine and arginine amino acid residues which bind with binds with the negatively charged phosphates in the DNA backbone. This interaction along with insertion of four bulky phenylalanine residues into the minor groove bends the DNA like a saddle. The correct answer is option D.