Abstract: Vectors which establish controlled expression of recombinant GHRH 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, 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.