Recombinant expression vector and lipid membrane structure having said vector encapsulated therein

[Problem] To provide a novel expression vector capable of effectively expressing a target protein in mitochondria and suppressing undesirable expression of the target protein in cell organelles other than mitochondria. [Solution] The present invention provides a recombinant expression vector for expressing a target protein in mitochondria of animal cells, and a lipid membrane structure having the vector encapsulated therein, wherein the recombinant expression vector has a promoter sequence exhibiting a transcription activity in the nuclei of animal cells, and has, under the control of the promoter sequence, a coding region which codes a target protein and includes one or more TGAs as codons corresponding to tryptophan. The recombinant expression vector according to the present invention can more efficiently and selectively express a target protein in mitochondria, and can be used as a more safe and effective drug for treating mitochondrial diseases.