DNA synthesis has progressed considerably since the first sequence was generated by phosphoramidite chemistry in the late 1970s, by Professor Marvin Caruthers. Today, with automation and algorithmic sequence prediction, artificial DNA synthesis is less prone to human error and can achieve higher accuracy. This allows scientists to create entirely custom genetic sequences without a DNA template to start with (sequence-independent) and the semi-rational or rational design of sequences and proteins or viral vectors used in precision medicine.
We are entering an age where the gene writing gap—the difference between technology’s genome reading capabilities with next-generation sequencing (NGS) and the ability to write long, complex DNA sequences—is closing rapidly. When planning your DNA synthesis projects, it’s vital to understand the role of newer approaches using automation and cell-free methods to achieve the target biological function. This article will also briefly cover the role of greener enzymatic methods that reduce reliance on harsh and hazardous organic solvents.
What is De Novo DNA Synthesis?
De novo DNA synthesis, or de novo DNA synthesis, is the process of chemically and/or enzymatically assembling double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) molecules in vitro. Unlike traditional cloning, which requires a pre-existing DNA template, de novo synthesis allows researchers to define target sequences entirely through computational design. The hierarchical process typically begins with the base-by-base construction of single-stranded oligonucleotides (oligos), which are then assembled into larger linear fragments or circular cloned products in cell-based expression systems, for the various applications of synthetic DNA.
Chemical DNA Synthesis
The prevailing standard for manufacturing oligonucleotides is phosphoramidite oligonucleotide synthesis (POS), a solid-phase method.1 This process involves a four-step elongation cycle: deprotection (using acid to remove 5′-DMT groups), coupling (adding the next nucleotide), capping (neutralizing unreacted strands), and oxidation (stabilizing the phosphate backbone). While POS is highly automated and indispensable, it suffers from several technical drawbacks. The recurring use of acid can cause depurination, a side reaction that removes purine bases and leads to strand breakage. Additionally, the reliance on organic solvents presents environmental challenges regarding waste disposal.
Enzymatic DNA Synthesis
To overcome the limitations of chemical methods, companies have developed Template-Independent Enzymatic Oligonucleotide Synthesis (TiEOS). This “green” technology utilizes the enzyme terminal deoxynucleotidyl transferase (TdT) to elongate DNA strands in an aqueous environment.2 Because TdT is naturally promiscuous, synthesis is controlled through reversible termination, where nucleotides are modified with a 3′-protecting group to ensure only one base is added per cycle. Enzymatic synthesis avoids the harsh acids of POS, resulting in higher-purity products and the potential to synthesize sequences that are traditionally difficult to produce chemically.
Cell-Free vs. Plasmid Synthesis
Traditional DNA manufacturing relies on cell-based systems, where synthetic fragments are cloned into plasmid vectors and transformed into bacteria for amplification and sequence verification. While effective, this process is labor-intensive and limited by the speed of biological growth. In contrast, cell-free technologies, such as Rolling Circle Amplification (RCA), use high-fidelity polymerases to amplify DNA without bacterial fermentation.3 Cell-free methods are significantly faster, and eliminate the risk of bacterial endotoxin contamination.
Limitations in Sequence Length
Synthesis length is primarily constrained by elongation cycle efficiency. Because each step of the synthesis process is less than 100% efficient, the theoretical yield of correct sequences plummets as strands grow longer; a 99% efficiency rate results in only a 13% yield for a 200-bp polymer. Beyond yield decay, long sequences (>3 kb) are prone to forming secondary structures like hairpins, which physically can block further elongation, and are therefore only possible to assemble using shorter building blocks. Assembly methods such as Gibson Assembly or Polymerase Cycling Assembly (PCA) are used to stitch smaller, high-fidelity oligonucleotides into genes, chromosomes, or entire synthetic genomes.
FAQ
- What is the typical length limit for oligonucleotides?Oligonucleotides synthesized via standard solid-phase methods aregenerally limited to lengths of less than 150 to 200 nucleotides. Beyond this point, the accumulation of point mutations and truncations makes the product difficult to use for precise biological applications. At Ribbon Bio, we assemble oligonucleotides together to achieve sequences up to 12 kb in length.
- Howaccurateare modern DNA synthesis platforms? Leading service providers now guarantee 100% sequence accuracy for clonal DNA products. This is achieved by using next-generation sequencing (NGS) to verify the sequence identity of synthesized fragments and filtering out any errors introduced during the assembly process. However accuracy decreases with length, and Ribbon Bio ensures the highest accuracy above traditional length limits of other providers.
- What are the advantages of cell-free vs. cell-based DNA synthesis?Cell-freesynthesis allows for one-shot protein production, and is able to scale with automation. Since it is bacteria-free, one can avoid bacterial contamination (from endotoxins) and the instability associated with certain genetic sequences in a living host. It can also produce proteins that would be cytotoxic to certain hosts.
- What are the applications of DNA synthesis?Synthetic DNA is used across a vast range of fields:
- Biomedicine:Vaccine development (mRNA templates), gene therapy, and diagnostic probes.
- Agriculture:Engineering heat-resistant or nutrient-efficient crops.
- Data Storage:Using the DNA alphabet (A, C, G, T) to store digital information at high density.
- Industrial:Optimizing microbial pathways for sustainable biofuel and chemical production.
- Beaucage, S. L., & Caruthers, M. H. (1981). Deoxynucleoside phosphoramidites—A new class of key intermediates for deoxypolynucleotide synthesis. Tetrahedron Letters, 22(20), 1859–1862.
- Palluk, S., & Arlow, D. H. et al. (2018). Template-Independent Enzymatic Oligonucleotide Synthesis (TiEOS) for DNA data storage and synthetic biology. Biochemistry, 57(22), 3109–3119.
- Nicholson, M. D. et al. (2020). Rolling circle amplification: A high fidelity and efficient alternative to plasmid preparation for infectious cDNA clones. PLOS ONE, 15(9), e0238155.
