In order to modify the regulatory region of a gene, we here developed a new standard by modifying the BioBricks standard and constructed a new genetic AND gate from standardized biological parts. The Lux-Lac AND gate we constructed is composed of LuxR and LacI operators, whose bindings to the regulatory proteins are controlled by AHL and IPTG, respectively. In order to realize the desired function, our AND gate has two important properties. One is that we prepared standardized parts, each of which has one operator site, and combined them by modular assembly. In contrast, another method of assembly in the synthetic Ara-lac AND gate  requires a unique DNA with multiple operator sites for each designed combination of parts. Another important property is that our method is based on the simple mechanism of gene regulation. It would be difficult to simultaneously use several complicated regulation assemblies such as a nonsense-suppression dependent system .
Our modification of BioBricks standard allows insertion of parts into an established assembly of other parts. Although In-Fusion BioBrick assembly reported very recently  may allow similar insertion of parts with further modifications of their method, it requires primers, each of which covers two parts next to each other in the design of an assembly. This combination-dependent synthesis reduces the utility of the established compatibility of each BioBricks part.
In contrast to design-based strategy we examined in this study, other researchers have used a combinatorial strategy to construct artificial biological devices. In order to establish the fine regulation of a genetic circuit, Guet et al. constructed a combinatorial library in which repressor coding sequence and promoters were connected in various orders on a plasmid . By using another combinatorial strategy, Cox III et al. constructed several AND gates and OR gates . In their study, operators for LacI, TetR, AraC, or LuxR were randomly inserted to the regulatory region. Though several gates were isolated, several nonfunctional gates were constructed at the same time. The design-based strategy is more effective for creating assemblies since it does not require huge resources. A hybrid strategy in which a combinatorial strategy and our strategy are combined would be effective to implement an artificial biological device with specific quantitative parameter dependence on inputs. In the combinatorial library, a regulatory protein should correspond to multiple operator parts, each of which has a different binding property for the protein.
The number of transcriptional factors and operators used in synthetic biology is increasing, and a combinatorial explosion in the number of possible assemblies must occur in the future. As a method to combat this combinatorial explosion, the design strategy assisted by computer simulations and mathematical models will be effective. Even though the wet-based method has middle-sized parallelism due to the number of cells screened, as indicated by the studies of DNA computer, it would consume a lot of molecules to solve a problem stemming from a combinatorial explosion. The parallelism in computer-based evaluation of assemblies is indeed much lower than that in wet-based evaluation, but the computer-based evaluation time for each assembly will be much shorter in the future. In addition, the activity predicted from computer design often could not correctly reflect the activity of a wet molecule in the present situation. In the future, however, technological advances will reduce the difference between the predicted value and the real value. Thus, computer-assisted rational design will become more effective than the combinatorial strategy.
The genetic logic gates established with our method or its modified version would make the cells recognize the pattern of multiple input-molecules. These engineered cells can be applied in drug-delivery systems, bioremediations, and material-synthesizing systems. A cell that recognizes a lot of inputs replies well to each situation. For example, engineered cells can be designed to release appropriate medicine inside patients upon recognizing tumour markers. Also, the cells that recognize the concentration of pollutants in the environment can be designed to absorb and degrade them. Cells that recognize the coexistence of key intermediates in a metabolic pathway can be designed to optimize the material-synthesizing system. To realize of such a technology, we must prepare a database of regulatory proteins each of which binds both of an input-molecule and an operator. Perhaps the Registry of Standard Biological Parts, which becomes larger and larger every year, is a good candidate database. The Registry of Standard Biological Parts would be more effective than other databases, such as Regulon DB, since the inventory of physical BioBricks parts and information in the database are linked together.