Bricks and blueprints: methods and standards for DNA assembly

Abstract

PrefaceDNA assembly is a key part of constructing gene expression systems and even whole chromosomes. In the past decade a plethora of powerful new DNA assembly methods including Gibson assembly, Golden Gate and LCR have been developed. In this Innovation article we discuss these methods and standards such as MoClo, GoldenBraid, MODAL and PaperClip, which have been developed to facilitate a streamlined assembly workflow, aid material exchange, and the creation of modular, reusable DNA parts. IntroductionOur capacity to cut and paste DNA from different sources and to assemble it into gene constructs has been one of the key drivers of biological research and biotechnology over the past four decades. However, despite countless advances in molecular biology, the assembly of DNA parts into new constructs remains a craft that is both time consuming and unpredictable. The decreasing costs of gene synthesis promises to alleviate these limitations by providing custom-made double-stranded DNA fragments typically between 200 and 2000 bp in length 1 . Nonetheless, gene synthesis does not eliminate the need for DNA assembly, which remains necessary for the production of constructs beyond one kilobase in size, both in research labs and at gene synthesis companies. DNA assembly also enables carrying out projects with more complex experimental needs and is especially valuable for building diverse plasmid libraries and creating multicomponent systems, and has even been used to construct synthetic cells 2 .Addressing the limitations of DNA assembly methods has been one of the key goals of synthetic biology, a scientific discipline focused on the construction and testing of new or redesigned versions of genes, gene networks, pathways and cells 3,4 . In order to tackle projects of increasing scale and complexity, researchers have invested significant effort into developing new tools for DNA assembly and into matching them with improved, lower-cost gene synthesis (for reviewes on gene synthesis see REFS. 1,5 1,5 ), as well as a suite of important new tools for genome editing (Box 1). With these combined advances the field is now at a point where gene synthesis and DNA assembly can empower even undergraduate students to construct entire eukaryotic chromosomes 6 . This acceleration in the scale of DNA assembly enables construction projects too complex to be drawn out on the back of an envelope, which instead require an engineering approach. In the past decade important 1 assembly methods such as Gibson assembly and Golden Gate have been developed 7,8 , which define new protocols for joining together DNA parts. Alongside these methods, researchers have also developed various physical standards such as MODAL (Modular Overlap-Directed Assembly with Linkers) 9 and MoClo (Modular Cloning system) 12 that define rules for the format of DNA parts that can be used with them. These physical standards facilitate the re-use of parts between experiments, exchange of parts between research groups and importantly provide modularity in construction. ...

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