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J. Virol., 02 1996, 1182-1190, Vol 70, No. 2
I Frolov and S Schlesinger
Alphaviruses, particularly Sinbis virus and Semliki Forest virus, are
proving to be useful vectors for the expression of heterologous genes. In
infected cells, these self-replicating vectors (replicons) transcribe a
subgenomic mRNA that codes for a heterologous protein instead of the
structural proteins. We reported recently that translation of the reporter
gene lacZ is enhanced 10-fold when the coding sequences of this gene are
fused downstream of and in frame with the 5' half of the capsid gene (I.
Frolov and S. Schlesinger, J. Virol. 68:8111-8117, 1994). The enhancing
sequences, located downstream of the AUG codon that initiates translation
of the capsid protein, have a predicted hairpin structure. We have mutated
this region by making changes in the codons which do not affect the protein
sequence but should destabilize the putative hairpin structure. These
changes caused a decrease in the accumulation of the
capsid-beta-galactosidase fusion protein. When these alterations were
inserted into the capsid gene in the context of the intact Sindbis virus
genome, they led to a decrease in the rate of virus formation but did not
affect the final yield. We also altered the original sequence to one that
has 12 contiguous G.C base pairs and should form a stable hairpin. The new
sequence was essentially as effective as the original had been in
enhancement of translation and in the rate of virus formation. The position
of the predicted hairpin structure is important for its function; an
insertion of 9 nucleotides or a deletion of 9 nucleotides decreased the
level of translation. The insertion of a hairpin structure at a particular
location downstream of the initiating AUG appears to be a way that
alphaviruses have evolved to enhance translation of their mRNA, and, as a
consequence, they produce high levels of the structural proteins which are
needed for virus assembly. This high level of translation requires an
intracellular environment in which host cell protein synthesis is
inhibited.
Copyright © 1996, American Society for Microbiology
Translation of Sindbis virus mRNA: analysis of sequences downstream of the initiating AUG codon that enhance translation
Department of Molecular Microbiology, Washington University, School of Medicine, St. Louis, Missouri 63110-1093, USA.
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