Reconstitution and Coupling of DNA Replication and Segregation in a Biomimetic System

Investigation of artificial cells containing the Par system for bacterial plasmid segregation and inheritance mimicry

A crucial step in life processes is the transfer of accurate and correct genetic material to offspring. During the construction of autonomous artificial cells, a very important step is the inheritance of genetic information in divided artificial cells. The ParMRC system, as one of the most representative systems for DNA segregation in bacteria, can be purified and reconstituted into GUVs to form artificial cells. In this study, we demonstrate that the eGFP gene is segregated into two poles by a ParM filament with ParR as the intermediate linker to bind ParM and parC-eGFP DNA in artificial cells. After the ParM filament splits, the cells are externally induced to divide into two daughter cells that contain parC-eGFP DNA by osmotic pressure and laser irradiation. Using a PURE system, we translate eGFP DNA into enhanced green fluorescent proteins in daughter cells, and bacterial plasmid segregation and inheritance are successfully mimicked in artificial cells. Our results could lead to the construction of more sophisticated artificial cells that can reproduce with genetic information.

Amplification of over 100 kbp DNA from Single Template Molecules in Femtoliter Droplets

Reconstitution of the DNA amplification system in microcompartments is the primary step toward artificial cell construction through a bottom-up approach. However, amplification of >100 kbp DNA in micrometer-sized reactors has not yet been achieved. Here, implementing a fully reconstituted replisome of Escherichia coli in micrometer-sized water-in-oil droplets, we developed the in-droplet replication cycle reaction (RCR) system. For a 16 kbp template DNA, the in-droplet RCR system yielded positive RCR signals with a high success rate (82%) for the amplification from single molecule template DNA. The success rate for a 208 kbp template DNA was evidently lower (23%). This study establishes a platform for genome-sized DNA amplification from a single copy of template DNA with the potential to build more complex artificial cell systems comprising a large number of genes.

Towards a synthetic cell cycle

Recent developments in synthetic biology may bring the bottom-up generation of a synthetic cell within reach. A key feature of a living synthetic cell is a functional cell cycle, in which DNA replication and segregation as well as cell growth and division are well integrated. Here, we describe different approaches to recreate these processes in a synthetic cell, based on natural systems and/or synthetic alternatives. Although some individual machineries have recently been established, their integration and control in a synthetic cell cycle remain to be addressed. In this Perspective, we discuss potential paths towards an integrated synthetic cell cycle.

Plasmid replication based on the T7 origin of replication requires a T7 RNAP variant and inactivation of ribonuclease H

T7 RNA polymerase (RNAP) is a valuable tool in biotechnology, basic research and synthetic biology due to its robust, efficient and selective transcription of genes. Here, we expand the scope of T7 RNAP to include plasmid replication. We present a novel type of plasmid, termed T7 ori plasmids that replicate, in an engineered Escherichia coli, with a T7 phage origin as the sole origin of replication. We find that while the T7 replication proteins; T7 DNA polymerase, T7 single-stranded binding proteins and T7 helicase-primase are dispensable for replication, T7 RNAP is required, although dependent on a T7 RNAP variant with reduced activity. We also find that T7 RNAP-dependent replication of T7 ori plasmids requires the inactivation of cellular ribonuclease H. We show that the system is portable among different plasmid architectures and ribonuclease H-inactivated E. coli strains. Finally, we find that the copy number of T7 ori plasmids can be tuned based on the induction level of RNAP. Altogether, this study assists in the choice of an optimal genetic tool by providing a novel plasmid that requires T7 RNAP for replication.

Bottom-Up Construction of Complex Biomolecular Systems With Cell-Free Synthetic Biology

Cell-free systems offer a promising approach to engineer biology since their open nature allows for well-controlled and characterized reaction conditions. In this review, we discuss the history and recent developments in engineering recombinant and crude extract systems, as well as breakthroughs in enabling technologies, that have facilitated increased throughput, compartmentalization, and spatial control of cell-free protein synthesis reactions. Combined with a deeper understanding of the cell-free systems themselves, these advances improve our ability to address a range of scientific questions. By mastering control of the cell-free platform, we will be in a position to construct increasingly complex biomolecular systems, and approach natural biological complexity in a bottom-up manner.

Reconstitution and Coupling of DNA Replication and Segregation in a Biomimetic System

A biomimetic system capable of replication and segregation of genetic material constitutes an essential component for the future design of a minimal synthetic cell. Here we have used the simple T7 bacteriophage system and the plasmid-derived ParMRC system to establish in vitro DNA replication and DNA segregation, respectively. These processes were incorporated into biomimetic compartments providing an enclosed reaction space. The functional lifetime of the encapsulated segregation system could be prolonged by equipping it with ATP-regenerating and oxygen-scavenging systems. Finally, we showed that DNA replication and segregation processes could be coupled in vitro by using condensed DNA nanoparticles resulting from DNA replication. ParM spindles extended over tens of micrometers and could thus be used for segregation in compartments that are significantly longer than bacterial cell size. Overall, this work demonstrates the successful bottom-up assembly and coupling of molecular machines that mediate replication and segregation, thus providing an important step towards the development of a fully functional minimal cell.