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Mol. Cell. Biol., Aug 1996, 4535-4543, Vol 16, No. 8
W Gu and NR Hecht
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.
Copyright © 1996, American Society for Microbiology
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
Department of Biology, Tufts University, Medford, Massachusetts 02155, USA.
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