Plasmid-based expression vectors, the most useful genetic tool in recombinant DNA technology, carry the foreign gene into the cell, and keep it stable, thereby enabling its expression within cells. These vectors typically have a replication origin, selection marker, and promoter as main genetic parts. Each of them enables chromosome-independent replication within cells, exerts pressure for the selection of recombinant cells, and controls the expression of carried foreign genes. Many studies have reported to design and improve vectors by using the targeted replacement and/or mutagenesis to the aforementioned major parts and spanning sequence. Despite the consistent reports on expression vectors with new functions, such approach has some constraints of using unstandardized genetic parts limited in functional sequence space. As an alternative, synthetic biology provides a foundation for tailor-made expression systems by rational design and modification via assembling various modular parts. Nevertheless, due to the limited number of modular parts and the lack of diversity of vector scaffold that offer the basis for assembly of these components, it falls short of constructing the expression systems feasible to graft into getting more useful expression system. This review will give a brief overview of the three major components and current status of vector design for expression of foreign genes, and then discuss the prospect of developing expression systems based on the systematic approaches, consequently expecting to understood the new platform for construction and improvement on target-ori-ented expression vectors via assembly of functional modules and scaffolds.

Precisely reliable and quantitative reporters can provide phenotypes that are consistent with research goals in protein expression. Here, we developed an improved reporter mATglu III 5 by directed evolution using a versatile β-glucosidase ATglu derived from Agrobacterium tumefaciens. When expressed in hosts, a vector containing this mutant distinctly showed a colored or fluorescent phenotype, according to the supplemented substrate, without any inducer. Analysis of mATglu III 5 showed it to be fully functional in fusion state with oligomeric proteins, especially under non-induction conditions, thereby offering an alternative to conventional reporters.