Translation of a testis-specific Cu/Zn superoxide dismutase (SOD-1) mRNA is regulated by a 65-kilodalton protein which binds to its 5' untranslated region.
Mouse testes contain two distinct superoxide dismutase (SOD-1) transcripts which differ by 114 nucleotides in their 5' untranslated regions (UTRs) (W. Gu, C. Morales, and N. B. Hecht, J. Biol. Chem. 270:236-243, 1995). The shorter SOD-1 mRNA, a somatic type SOD-I mRNA (SSOD-1), is ubiquitously expressed in all somatic tissues as well as in testes. The larger SOD-1 mRNA, a testis-specific SOD-1 mRNA (TSOD-1), derived from an alternative upstream start site, is transcribed solely in postmeiotic germ cells and is translationally regulated during spermiogenesis. Since the two mRNAs have identical nucleotides except that TSOD-1 has an additional sequence at its 5' terminus, we have proposed that the extra 5' UTR sequence may be involved in the translational control of the TSOD-1 mRNA during spermiogenesis. Here we show that, when assayed in a cell-free system, TSOD-1 is translated only slightly less efficiently than SSOD-1. RNA gel retardation and UV cross-linking assays reveal that a testicular cytoplasmic protein (Cu/Zn superoxide dismutase RNA-binding protein [SOD-RBP]) of about 65 kDa specifically binds to the extended 5' UTR of TSOD-1. After purification of SOD-RBP by RNA affinity chromatography, we demonstrate that SOD-RBP can repress the in vitro translation of TSOD-1 mRNA but not SSOD-1 mRNA or cotranslated luciferase mRNA. We conclude that SOD-RBP serves as a repressor in the translation of TSOD-1 mRNA during spermiogenesis and thereby fine-tunes the level of Cu/Zn superoxide dismutase produced in maturing germ cells.
Gu
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Department of Biology, Tufts University, Medford, Massachusetts 02155, USA.
Hecht
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D000595:Amino Acid Sequence; D000818:Animals; D002474:Cell-Free System; D003432:Cross-Linking Reagents; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D013091:Spermatogenesis; D013482:Superoxide Dismutase / Q000235:genetics*; D013737:Testis / Q000201:enzymology*; D014018:Tissue Distribution
D003432:Cross-Linking Reagents; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D013482:Superoxide Dismutase