Alternative polyadenylation sites

Exact pre-mRNAs hold more than single group of signal sequences for 3' end polyadenylation and cleavage.   In  some  cases,  the  area  of  the  instead polyadenylation   sites  is  like  which,  depending  on  the  site  chosen,  certain exons should be lost or retained in the subsequent  splicing reactions that is shown in the figure. Here the effect is to change  the coding  capacity  of the last mRNA  so which variant proteins  are  formed  depending  on  the  polyadenylation   site  used.  In  other cases,  the instead  sites both  lie within  the 3'  noncoding  region  of the pre- mRNA so in which the same coding sequences  are involved in the last mRNA irrespective of that site is used but the 3'  noncoding region can vary. Since the 3' noncoding series should have signals to control mRNA stability, the choice of polyadenylation site in this location can affect the lifetime of the resulting mRNA.

Figure:  Use of alternative polyadenylation sites.