Human CuZn superoxide dismutase enzymatic activity in cells is regulated by the length of the mRNA.

Single functional human CuZnSOD gene encodes two species of mRNA differing in size by 200 nucleotides in the 3'-untranslated region (UTR). We studied the expression of the CuZnSOD cDNA with different 3'- and 5'-UTR. Deletion in the 5'-end does not affect the expression of the enzyme, however, deletion in the 3'-UTR decreases the level of expression of CuZnSOD. The plasmids containing the long CuZnSOD cDNA with all polyadenylation signal sequences utilize primarily the last polyadenylation site and give a long mRNA, which produces three times more enzyme than the short mRNA lacking the last polyadenylation site and the AU-rich region.