Polyadenylation is a process that pertains to the expression of almost all genes in eukaryotes. In addition, as is the case with virtually every step in the process, polyadenylation is a step at which regulation may occur. The most obvious way by which this might occur is via what is commonly known as alternative polyadenylation. Alternative polyadenylation, in a nutshell, involves the use of alternative poly(A) sites within a single gene. The general idea is shown in Figure 1 – any gene that has more than one poly(A) site has the potential to be processed at any of the various sites.
Posted by Arthur Hunt 
The RNA Underworld 