In response to T cell activation signals, the half-life of interleukin-2 (IL-2) mRNA is greatly extended. The cis elements mediating IL-2 mRNA stabilization are located in its 5' and 3' untranslated regions (UTR). The 3'UTR also contains AU-rich elements (AREs) that mediate rapid IL-2 mRNA degradation in the cytoplasm of nonstimulated T cells. NF90, a previously described RNA binding protein, binds to a subregion of the 3'UTR that contains several AREs and slows down the degradation of IL-2 mRNA. In nonstimulated cells, NF90 is mostly nuclear, but T cell activation results in its accumulation in the cytoplasm. The nuclear export of NF90 is required for IL-2 mRNA stabilization.