IN MALE-MOUSE GERM-CELLS, COPPER-ZINC SUPEROXIDE-DISMUTASE UTILIZES ALTERNATIVE PROMOTERS THAT PRODUCE MULTIPLE TRANSCRIPTS WITH DIFFERENT TRANSLATION POTENTIAL

Copper zinc superoxide dismutase (SOD-1) is an enzyme that is widely expressed in eukaryotic cells and performs a vital role in protecting cells against free radical damage. In mouse testis, three different sizes of SOD-l mRNAs of about 0.73, 0.80, and 0.93 kilobases (kb) are detected. The 0.73-kb mRNA is found in early stages of male germ cells and in all somatic tissues. The mRNAs of 0.80 and 0.93 kb are exclusively detected in post-meiotic germ cells. RNase H digestions and Northern blot analyses reveal that the three SOD-l mRNAs are derived from two transcripts, a ubiquitously expressed transcript and a post-meiotic transcript, which differ by 114-120 nucleotides. RNase protection assays demonstrate that the additional nucleotides present in the post-meiotic mRNA are solely in the 5'-untranslated region. Using a probe derived from the 5'-untranslated region of the 0.93-kb SOD-l mRNA, we have established that it originates from an alternative upstream promoter contiguous with the somatic SOD-l promoter. Polysomal gradient analysis of the three mouse testis SOD-1 mRNAs reveals that the 0.93-kb SOD-l mRNA is primarily non-polysomal, while the 0.80 and 0.73 kb SOD-l mRNAs are mostly polysome associated. A faster migrating form of the 0.93-kb SOD-l mRNA is present on polysomes as a result of partial deadenylation. In a cell-free translation system, the 0.73-kb SOD-1 mRNA translates about 2-fold more efficiently than the 0.93 kb SOD-l mRNA These data demonstrate that male germ cells transcribe two size classes of SOD-1 mRNAs with different translation potential by utilizing two different promoters, post meiotic SOD-1 mRNAs undergo adenylation changes, and one of the post-meiotic SOD-l mRNAs is transcribed during mid-spermiogenesis and translated days later in a partially deadenylated form.