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Mol. Cell. Biol., Dec 1995, 6593-6600, Vol 15, No. 12
MK Phillips-Jones, LS Hill, J Atkinson and R Martin
The effect of the 3' codon context on the efficiency of nonsense
suppression in mammalian tissue culture cells has been tested. Measurements
were made following the transfection of cells with a pRSVgal reporter
vector that contained the classical Escherichia coli lacZ UAG allele YA559.
The position of this mutation was mapped by virtue of its fortuitous
creation of a CTAG MaeI restriction enzyme site. Determination of the local
DNA sequence revealed a C-->T mutation at codon 600 of the lacZ gene:
CAG-->TAG. Site-directed mutagenesis was used to create a series of
vectors in which the base 3' to the nonsense codon was either A, C, G, or
U. Suppression of the amber-containing reporter was achieved by
cotransfection with genes for human tRNA(Ser) or tRNA(Gln) UAG nonsense
suppressors and by growth in the translational error-promoting
aminoglycoside drug G418. Nonsense suppression was studied in the human
cell lines 293 and MRC5V1 and the simian line COS-7. Overall, the rank
order for the effect of changes to the base 3' to UAG was C < G = U <
A. This study confirms and extends earlier findings that in mammalian cells
3' C supports efficient nonsense suppression while 3' A is unsympathetic
for read-through at nonsense codons. The rules for the mammalian codon
context effect on nonsense suppression are therefore demonstrably different
from those in E. coli.
Copyright © 1995, American Society for Microbiology
Context effects on misreading and suppression at UAG codons in human cells
Krebs Institute for Biomolecular Science, University of Sheffield, United Kingdom.
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