Functions of the 3′untranslated regions (3′UTR) of eukaryotic mRNAs are complicated. They can control the stability and intracellular localization of mRNAs, and direct the translation of special amino acids. Mutations in the 3′UTR of some mRNA can cause serious diseases, and recent studies showed that the 3′UTR of some eukaryotic mRNAs possess tumor-suppression function.