#Question id: 4459

Give correct explanation, why RNA polymerase can initiate a new RNA chain on a DNA template without any primer?

A. Because RNA polymerase starts most transcripts with an A, and that ribonucleotide binds the template nucleotide (T) with only two hydrogen bonds.

B. The enzyme has to make specific interactions with one or all of the DNA template strand, the initiating ribonucleotide, and the second ribonucleotide—holding one (or all) rigidly in the correct orientation to allow chemical attack on the incoming NTP.

C. The structure of the open complex shows that the s region 3/4 linker interacts with the template strand, organizing it in the correct conformation and location to allow initiation.

D. Consistent with this, in experiments using an RNA polymerase containing a s70 derivative lacking this part of s, initiation requires much lower than normal concentrations of one or both of the first two ribonucleotides.