NATIONAL SCIENCE FOUNDATION
U.S. DEPARTMENT OF EDUCATION
The final step in processing pre-mRNA
is the addition of a poly(A) tail to its 3' end. Clicking
on each of the thumbnail images will bring up a larger, labeled
version of the described scene.
see the Flash movie for the following sequence of images,
After cleavage, PAP slowly begins to create
the poly(A) tail.
After the tail has reached a short length,
additional proteins bind to the mRNA and increase the rate
at which the tail grows.
When the tail has reached its full length,
PAP is signaled to stop adding A residues, and the tail is
The result of mRNA processing is a strand
of mRNA, complete with cap and poly(A) tail, ready for splicing.