Alternative polyadenylation sites:

Definite pre-mRNAs hold more than one 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,  particular exons should be lost or retained in the subsequent  splicing reactions that is shown in the figure. Here the effect is to modify the coding capacity of the last mRNA  so which variant proteins  are  produced  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 similar 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 sequence should contain 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.