Elongation is the stage of transcription
in which the Pol II complex creates a complementary strand of mRNA. Once the
entire transcription unit has been 'copied', the Pol II must release the newly
finished strand of mRNA. The general transcription factors involved in the process
also release during or at the end of this stage of transcription. Clicking
on each of the thumbnail images will bring up a larger, labeled version of the
see the Flash movie for the following sequence of images,
Once the ATP have been added, an 'eye' opens
in the DNA giving access to the DNA template, and the creation of mRNA can
Once mRNA elongation begins, TFIIE (olive green) and
TFIIH (red) are released. Also released at this time are TFIIA and TFIIB
TFIIE is shown moving into the distance, and the mRNA
strand is elongating rapidly.
Elongation of the mRNA stops when the end of the transcription
unit is reached.
As elongation stops, the DNA 'eye' closes.
The Pol II complex is now released from the DNA, along
with the phosphates added to it by the ATP.
As the Pol II complex dissociates from the DNA, the
mRNA strand is released. At this time, TFIID also unbinds from the DNA,
allowing the DNA to return to its normal shape.
Transcription is now complete. An mRNA copy has been
produced and is now ready to be moved outside of the nucleus and be used
in the translation process.