NATIONAL SCIENCE FOUNDATION
U.S. DEPARTMENT OF EDUCATION
When mRNA is ready for splicing, it is known as a primary transcript. 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,
The primary transcript contains sequences known as exons and introns.
This primary transcript contains two exons and one intron. Here we see exon 1.
Here we see the intron. Introns contain sequences that guide the splicing process. These include a 5' GU (GT in DNA) sequence...
...an A branch site located near a pyrimidine-rich region...
...and a 3' AG sequence.
Exon 2 is found on the opposite end of the intron. The 3' end of the primary transcript also contains the poly-A tail added during mRNA processing.
--> 2.) SPLICEOSOME