Transcription begins with a strand of DNA.

It is divided into several important regions.

The largest of these is the transcription unit.

This portion of the DNA will be used to produce RNA.

Upstream of the transcription unit is the TATA box.

An enhancer region may also be involved.

Several complexes, known as transcription factors,

are required for successful transcription.

The first is TFIID,

the largest of the general factors.

A component of this factor, TBP,

binds to the DNA

using the TATA box to position TFIID

near the transcription initiation site.

Other transcription factors,

including TFIIA and TFIIB, then attach.

These complexes prepare the DNA

for the successful binding of RNA polymerase.

Once RNA polymerase is bound,

other transcription factors complete the mature transcription complex.

Now, energy must be added to the system for transcription to begin.

This energy is provided by the reduction of ATP

into ADP and Pi.

RNA polymerase then synthesizes an RNA template

from the strand of DNA.

Most factors are released after transcription begins.

When the end of the transcription unit is reached,

the RNA polymerase dissociates,

and the newly formed strand of RNA is released.