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Mol. Cell. Biol., Jul 1996, 3523-3534, Vol 16, No. 7
S McBratney and P Sarnow
The molecular mechanism with which an appropriate AUG codon is selected as
the start site for translational initiation by eukaryotic ribosomes is not
known. By using a cell-free translation system, small RNA molecules
containing single AUG codons, surrounded by various nucleotide sequences,
were tested for their abilities to interfere with the translation of a
reporter mRNA. RNAs containing the AUG in an ACCAUGG context (Kozak
consensus sequence) were able to inhibit translation of the reporter mRNA.
In contrast, RNAs containing the AUG in a less favorable context for start
site selection (for example, CAGAUGG) had no effect on the translation of
the reporter mRNA. The effect mediated by the ACCAUGC-containing RNAs was
not due to sequestration of ribosomal subunits or to particular structural
features in these RNAs. To identify potential trans-acting factors that
might be preferentially bound by ACCAUGG-containing RNAs, ACCAUGG- and
CAGAUGC-containing RNAs with a single 4-thiouridine residue at the AUG were
incubated with partially fractionated extracts, and AUG-binding proteins
were identified after irradiation of the complexes with UV light and
subsequent analysis by gel electrophoresis. The analysis (of such complexes
in competition experiments revealed that proteins, approximately 50 and 100
kDa in size, were found to bind directly at the AUG codon embedded in the
ACCAUGG motif. One of these proteins has been identified as the La
autoantigen. These findings indicate that trans-acting factors may play a
role in AUG start site selection during translational initiation.
Copyright © 1996, American Society for Microbiology
Evidence for involvement of trans-acting factors in selection of the AUG start codon during eukaryotic translational initiation
Molecular Biology Program and Department of Biochemistry, Biophysics and Genetics, University of Colorado Health Sciences Center, Denver, 80262, USA.
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