Figure 2.

Cis-elements and polyadenylation factors. Light-green boxes represent cis-elements in the pre-mRNA and light-purple boxes represent polyadenylation factors. The endonucleolytic cleavage of the pre-mRNA is made by the CPSF-subunit CPSF-73 at the poly(A) site, typically immediately 3′ of a CA dinucleotide. After cleavage, an untemplated poly(A) tail of about 250 adenosine-nucleotides, is added to the upstream cleavage product by PAP. This is stimulated by the CPSF through the nuclear poly(A)-binding protein (PABPN1) which binds the growing poly(A) tail and controls its length.