Vector Design for Optimal Protein Expression

Many DNA constructs are generated for protein expression studies. Translational properties and mRNA stability are crucial aspects that have to be accounted for during DNA construction. An optimized vector for protein overexpression studies is described considering elements in the mature mRNA that influence translatability and stability. Recommendations regarding vector construction for Xenopus laevisembryo injection are provided, based on literature and experimental data. The 5′ untranslated region (5′UTR) should be non-regulated, short, unstructured, and without AUG codons. The sequence around the start codon should match the initiation context of the species studied (ACCAUGG, for vertebrates), and the open reading frame should be cloned with its own stop codon, followed by a G or A residue. Furthermore, the 3′UTR should be non-regulated, and a strong polyadenylation signal must be included in DNA vectors. In RNA template vectors, the presence of a poly(A) or AC tail is essential for stability, as well as for translation efficiency in mRNA injection experiments. These aspects result in high-level expression of exactly the desired protein. Easily obtainable examples of the sequences [5′UTR, 3′UTR, and poly(A) signal] are suggested.