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same sequence as the mRNA and
is related by the genetic

code to the protein sequence that it represents.
The antisense strand (Template strand) of DNA is complementary to the sense
strand, and is the one that acts as the template for synthesis of mRNA.
RNA polymerases are enzymes that synthesize RNA using a DNA template
(formally described as DNA-dependent RNA polymerases).
A promoter is a region of DNA where RNA polymerase binds to initiate
transcription.
Startpoint (startsite) (Startsite) refers to the position on DNA corresponding to the
first base incorporated into RNA.
A terminator is a sequence of DNA that causes RNA polymerase to terminate
transcription.
A transcription unit is the distance between sites of initiation and termination by
RNA polymerase; may include more than one gene.
Upstream identifies sequences proceeding in the opposite direction from expression;
for example, the bacterial promoter is upstream of the transcription unit, the
initiation codon is upstream of the coding region.
Downstream identifies sequences proceeding farther in the direction of expression;
for example, the coding region is downstream of the initiation codon.
A primary transcript is the original unmodified RNA product corresponding to a
transcription unit.

DNA ·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.

the 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.

-7 to -11 of the promoter while positions -1 to

-4 enter the active site.

makes 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.

the 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.

II from yeast shows that DNA is surrounded by ~270°

of protein.

site 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