This invention relates to gene therapy by using vectors which encode stable MRNA and methods of using such vectors. In particular, this invention relates to vectors which establish controlled expression of recombinant genes within tissues at certain levels. The vector includes a 5' flanking region which includes necessary sequences for expression of a nucleic acid cassette, a 3' flanking region including a 3' UTR and/or 3' NCR which stabilizes mRNA expressed from the nucleic acid cassette, and a linker which connects the 5' flanking region to a nucleic acid sequence. The linker has a position for inserting a nucleic acid cassette. The linker does not contain the coding sequence of a gene that the linker is naturally associated with. The 3' flanking region is 3' to the position for inserting the nucleic acid cassette. The expression vectors of the present invention can also be regulated by a regulatory system and/or constructed with a coating.
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