DNA has a beautiful symmetrical structure called a double helix structure. DNA has a robust structure and, based on sequence information, can change its mechanical properties such as shape and hardness, and can also exhibit dynamic phenomena such as chemical reactions and phase separation. At present, the thermodynamic behavior of DNA double-helix formation can be easily predicted by computer using free energy calculations, and it is possible to design not only static structures but also non-equilibrium dynamic behaviors including chemical reactions.

DNA is a unique material with characteristic multi-scale molecular and informational properties. Single-stranded DNA is a flexible string that bends after 1 nm or so, but in the case of double-helix structure, it becomes as rigid as a 60-nm rod. Using DNA nanotechnology, it is possible to synthesize robust structures as rigid as the order of 1 μm. In addition, chromosomal DNA is in a fluid and dynamic gel/liquid state in the cell nucleus, aggregating to several micrometers in length, while in the relaxed coiled state it is as long as 1 m. The long double-helix structure of chromosomal DNA is stabilized by the quantum phenomenon π-π interaction between bases, which lasts for long distances. Such a long double-helix structure is also interesting from a physical point of view because of the strong effect of a quantum mechanical phenomenon of electrons, namely π-π interactions between bases, on the stabilization of such a long-distance double helix structure. On the other hand, it is not only possible to accurately store large amounts of information on tens of thousands of genes in such a small material, but also to create nanocomputers/nanodevices and large-capacity storage (~1 billion TB/g) that is expected to be stable for tens of thousands of years. In this sense, DNA is a molecule that embodies the concept that “Life = Matter x Information”.

Furthermore, cells are tiny droplets (capsules) in volumes ranging from fL to pL, and at such small scales, effects such as droplet interfacial tension and surface charge, molecular size and crowding effects, molecular fewness and reaction fluctuations, strong nonlinearity and non-equilibrium feature, and other influences that are not present in a mL-sized test tube reaction, appear. How living systems can achieve stable, efficient and accurate molecular information processing in chemical reactions in such complex and strongly fluctuating systems is of interest from a life science perspective, but it is also an important question from a physical and information science perspective when considering the creation of a nano-sized molecular computer.

Living systems are the unique material systems that have evolutionally acquired the ability to use matter for information processing and the ability to manipulate matter using information. In other words, the living system have demonstrated the capabilities of computation using physical and chemical phenomena and of performing physical and chemical work through computation (this idea is called natural computing). Approaching the physical and chemical principles of natural computing is expected to advance our understanding of the physics of information and the development of new nanocomputers.

From the perspective above, we have been actively researching the following in recent years.

• ・Construction of artificial cell nuclei (artificial chromosomes) using DNA nanotechnology
• ・Biophysical research such as the quantitative analysis of RNA using an artificial chromatin model and mathematical model and reconstitution experiments of chromosome segregation
• ・Coarse-grained Brownian dynamics simulation of DNA gels and DNA droplets
• ・Sequence design of DNA gel by reinforcement learning
• ・Research on molecular computers and molecular memory with digital-to-molecular information conversion
• ・Construction of cellular molecular robots using DNA nanostructures
• ・Development of molecular robots that mimic macrophages (one of immune cells)
• ・Emergence of Spontaneous motion of micro-materials under nonequilibrium electron transfer using charged nano-micelles
• ・Spontaneous ratchet transport of micro-materials using particle crowding effects
• ・Computer-aided control of artificial cell reactors
• ・Tiny non-equilibrium open reactors and artificial-nucleus transcriptional oscillators in the reactor