Транскрипция

·RNA polymerase separates the two strands of DNA in a transient "bubble" and uses one strand as a template to direct synthesis of a complementary sequence of RNA.The length of the bubble is ~12-14 bp, and the length of RNA-DNA hybrid within it ~8-9 bp.

first bond in RNA. This includes binding of RNA polymerase to the promoter and melting a short region of DNA into single strands.
Elongation is the stage in a macromolecular synthesis reaction (replication, transcription, or translation) when the nucleotide or polypeptide chain is being extended by the addition of individual subunits. During elongation the transcription bubble moves along DNA and the RNA chain is extended in the 5’ – 3’ direction.
Termination is a separate reaction that ends a macromolecular synthesis reaction (replication, transcription, or translation), by stopping the addition of subunits, and (typically) causing disassembly of the synthetic apparatus. Transcription stops, the DNA duplex reforms and RNA polymerase dissociates at a terminator site.

to -11 of the promoter while positions -1 to -4 enter the active site.

a sharp turn at the active site. A protein bridge changes conformation to control the entry of nucleotides to the active site.

The b (cyan) and b’ subunit (pink) of RNA polymerase have a channel for the DNA template. Synthesis of an RNA transcript (copper) has just begun; the DNA template (red) and coding (yellow) strands are separated in a transcription bubble.

crystal structure. The colors of the subunits are the same as in the crystal structures of the following figures.

The side view of the crystal structure of RNA polymerase II from yeast shows that DNA is
held downstream by a pair of jaws and is clamped in position in the active site, which contains an Mg++ ion.

from yeast shows that DNA is surrounded by ~270° of protein.

by a wall of protein. Nucleotides may enter the active site through a pore in the protein

An expanded view of the active site shows the sharp turn in the path of DNA