Splicing signal

Virtualab Protocols (Chang Bioscience)
1. Most introns start with GU and end with AG. A small fraction of introns start with AT and ends with AC.

2. The branch site is located 20-50 bases upstream of the acceptor site.

5'-splice site
Branch site 3'-splice site
A/C A G G U Pu A G U          C U Pu A Py      Py rich    N C A G G

Pu = A or G, Py = C or U, and N = Pu or Py.