Me. Moustafa et al., OVERPRODUCTION OF SELENOCYSTEINE TRANSFER-RNA IN CHINESE-HAMSTER OVARY CELLS FOLLOWING TRANSFECTION OF THE MOUSE TRNA([SER]SEC) GENE, RNA, 4(11), 1998, pp. 1436-1443
Selenocysteine insertion during selenoprotein biosynthesis begins with
the aminoacylation of selenocysteine tRNA([Ser]Sec) with serine, the
conversion of the serine moiety to selenocysteine, and the recognition
of specific UGA codons within the mRNA. Selenocysteine tRNA([Ser]Sec)
exists as two major forms, differing by methylation of the ribose por
tion of the nucleotide at the wobble position of the anticodon. The le
vels and relative distribution of these two forms of the tRNA are infl
uenced by selenium in mammalian cells and tissues. We have generated C
hinese hamster ovary cells that exhibit increased levels of tRNA([Ser]
Sec) following transfection of the mouse tRNA([Ser]Sec) gene. The leve
ls of selenocysteine tRNA([Ser]Sec) in transfectants increased proport
ionally to the number of stably integrated copies of the tRNA([Ser]Sec
) gene. Although we were able to generate transfectants overproducing
tRNA([Ser]Sec) by as much as tenfold, the additional tRNA was principa
lly retained in the unmethylated form. Selenium supplementation could
not significantly affect the relative distributions of the two major s
elenocysteine tRNA([Ser]Sec) isoacceptors. In addition, increased leve
ls of tRNA([Ser]Sec) did not result in measurable alterations in the l
evels of selenoproteins, including glutathione peroxidase.