The present invention relates to RNA vectors comprising alphavirus RNA having inserted therein a recombinant retrovirus genome containing a foreign RNA sequence encoding a biologically active substance. The vectors of the present invention provide for the high level expression of the recombinant retrovirus genome directly in the cell cytoplasm of eukaryotic cells. When coexpressed with structural proteins of the retrovirus, the recombinant genome can efficiently be packaged into infectious recombinant retrovirus, also called retrovirus vectors, which can transduce the foreign RNA into recipient cells. Most importantly this cytoplasmic expression system facilitates the efficient production of vectors containing foreign RNA comprising genes in combination with introns or other control elements of gene expression. Such vectors have been impossible or very difficult to produce by the conventional nuclear expression systems because of RNA splicing.
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