Abstract: A method for trans-splicing peptides is provided. In the method, at least two extein peptides are provided, or are synthesized by recombinant methods, the extein peptides having co-reacting portions of a split intein attached thereto, so that the peptides will splice automatically under suitable conditions. A vector is also provided which includes at least one extein gene for expressing at least one of the extein peptides. Further provided is a method for circumventing packaging limitations in a gene delivery vehicle, by splitting a coding region for a protein to be delivered into two or more extein genes, which are packaged in separate virus particles and are co-delivered to a target cell for expression and for subsequent trans-splicing to form the complete protein. A pharmaceutical composition and a therapeutic method are also provided in which the recombinant viral particles are delivered to a cell and are expressed to produce a trans-spliced protein.