ology is called “synthetic biology” [ 6]. Synthetic biology researchers try to construct artificial systems by remodeling existing cells such as E. coli. The difference between genetic engineering and synthetic biology may not be immediately obvious. Genetic engineering essentially tries to add a single function by inserting a gene into a cell. Synthetic biology, on the other hand, tries to add a system to a cell.

An illustrative example in synthetic biology is the creation of a concentration band detector by Basu and his colleagues [ 1]. See Figures 1 and 2. They implemented a system that included a sensor to measure the concentration of a specific substance in the outside environment. The system then judges whether the concentration is within a specific range.

This determination is made by a genetic circuit consisting of several genes. If the concentration is within the range of interest, the green fluorescent protein (GFP) gene is expressed and cells containing the gene glow. The system consists of all three components: the sensor, computer, and actuator, along with the GFP gene. The system is implemented inside E. coli cells. More specifically, a plasmid (small chromosome) that contains the necessary genes is inserted into E. coli cells.

Synthetic biology clearly has a close relationship with bioinformatics, which is already a mature research field in which IT is used to analyze living organisms. It ranges from methods for analyzing genetic sequences in genome chromosomes to those for modeling and simulating biological networks as complex systems. The latter approaches comprise the currently active research field called systems biology, which tries to capture biological phenomena from the point of systems science. However, even systems biology focuses mainly on analyzing existing living organisms. In other words, systems biology is a kind of reverse engineering that tries to understand natural systems inside cells, while synthetic biology is forward (i.e., ordinary) engineering that tries to implement artificial systems in cells.

The purpose of synthetic biology may not be clear. As noted above, input

Figure 1: The band-detect multicellular system programs E.coli receiver cells to fluoresce only at intermediate distances from sender cells. See Basu [ 1] for more.

Reprinted by permission from Macmillan Publishers Ltd: Nature [ 1], copyright 2005.

 

to and output from cells are usually chemical substances. Therefore, by remodeling cells, the creation of useful artificial systems that sense chemical signals and produce chemical output is possible. For example, one could imagine bacteria that can search for cancer by sensing signals from cancer cells and destroying the cancer cells by producing appropriate drugs.

DNA NANO TECHNOLOGY Although making artificial systems out of cells is nice, smaller systems that could serve similar functions as those of cells would be better. For example, viruses are much smaller than cells but are still capable of specific functions, such as chromosome insertion. Therefore, nanotechnology researchers are also focusing on constructing autono-