In mouse, the antrum is the major site of gastrin expression. Duodenum also express gastrin, but the level of expression is low. Mouse gastrin mRNA has AAUAAG sequence as a putative polyadenylation signal rather than AAUAAA. Thus the gastrin expression level of mouse is lower than that of rat. Although the cleavage efficiency is relatively low, once they have been cleaved even with AAUAAG sequence, they are polyadenylated as efficiently as with AAUAAA. In the tissue, unprocessed RNA transcripts are rapidly degraded. Only processed RNAs are transported to cytoplasm. The duplicated CAUGU and GGAGAGGGGUUG, homologous to CAYUG and GT-rich sequence, are located at 25 and 43 nucleotides downstream from AAUAAG sequence. These sequence may function as downstream poly(A) addition signals. Thus mouse gastrin mRNA in the antral and duodenal tissue are normally processed, although the efficiency of processing is relatively lower than other mammalian species possessing AAUAAA as poly(A) addition signal.