This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
What is the function of a promoter site on DNA? 
Select and explain. 
A. Transcribes repressor, B. Initiates transcription, C. Codes for RNA polymerase, D. Regulates termination
B: Initiates transcription
Answer: B: Initiates transcription 
Explanation: Promoter sites are initiation sites for transcription. Transcription stas when RNA polymerase binds to the promoter. It then unwinds the closed promoter complex, where DNA is in the form of a double helix, to form the open promoter complex in which about 17 base pairs of template DNA are unwound. RNA synthesis then begins with either a pppA or a pppG inseed at the beginning 5'-terminus of the new RNA chain, which is synthesized in the 5' to 3' direction. Ref: Weil P. (2011). Chapter 36. RNA Synthesis, Processing, & Modification. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds),Harper's Illustrated Biochemistry, 29e.