Before transcription of the DNA molecule can
begin, certain factors must be present. These factors are responsible for altering
the DNA in preparation for the actual transcription. Clicking on each
of the thumbnail images will bring up a larger, labeled version of the described
see the Flash movie for the following sequence of images,
Transcription begins with a strand of DNA.
This simplified DNA model has been color-coded to show regions with important
roles in transcription.
The largest key region is the transcription unit.
Upstream of the transcription unit is the TATA-box,
a smaller section that helps to position the complexes involved in transcription.
The final high-lighted region is the enhancer.
TFIID, a general transcription factor,
is shown approaching the strand of DNA.
TFIID is the largest of the general transcription factors
involved in eukaryotic transcription. The yellow part of the complex is
TBP (yellow) binds to the DNA, using the TATA-box to
position itself near the iniation site of transcription.
When the TBP portion of the TFIID molecule attaches to
the TATA-box, its shape causes the DNA to bend.