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Mol. Cell. Biol., Apr 1997, 1977-1985, Vol 17, No. 4
A Lesoon, A Mehta, R Singh, GM Chisolm and DM Driscoll
In mammalian selenoprotein mRNAs, the recognition of UGA as selenocysteine
requires selenocysteine insertion sequence (SECIS) elements that are
contained in a stable stem-loop structure in the 3' untranslated region
(UTR). In this study, we investigated the SECIS elements and cellular
proteins required for selenocysteine insertion in rat phospholipid
hydroperoxide glutathione peroxidase (PhGPx). We developed a translational
readthrough assay for selenoprotein biosynthesis by using the gene for
luciferase as a reporter. Insertion of a UGA or UAA codon into the coding
region of luciferase abolished luciferase activity. However, activity was
restored to the UGA mutant, but not to the UAA mutant, upon insertion of
the PhGPx 3' UTR. The 3' UTR of rat glutathione peroxidase (GPx) also
allowed translational readthrough, whereas the PhGPx and GPx antisense 3'
UTRs did not. Deletion of two conserved SECIS elements in the PhGPx 3' UTR
(AUGA in the 5' stem or AAAAC in the terminal loop) abolished readthrough
activity. UV cross-linking studies identified a 120-kDa protein in rat
testis that binds specifically to the sense strands of the PhGPx and GPx 3'
UTRs. Direct cross-linking and competition experiments with deletion mutant
RNAs demonstrated that binding of the 120-kDa protein requires the AUGA
SECIS element but not AAAAC. Point mutations in the AUGA motif that
abolished protein binding also prevented readthrough of the UGA codon. Our
results suggest that the 120-kDa protein is a significant component of the
mechanism of selenocysteine incorporation in mammalian cells.
Copyright © 1997, American Society for Microbiology
An RNA-binding protein recognizes a mammalian selenocysteine insertion sequence element required for cotranslational incorporation of selenocysteine
Department of Cell Biology, The Cleveland Clinic Foundation, Ohio 44195, USA.
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