Breakthrough Discovery: DNA Polymerases Caught 'Doodling' New Genetic Sequences

Researchers at the University of Bristol have uncovered a remarkable hidden capability of DNA polymerases, the molecular machines responsible for copying genetic information during cell division. In a study published in Nature Communications, the team demonstrated that these enzymes can generate entirely new DNA sequences without a guiding template—a process dubbed 'doodling'. This finding not only deepens our understanding of how genetic material might evolve but also opens doors to revolutionary methods for synthesizing long DNA strands in the lab.

DNA polymerases, often likened to nature's photocopiers, ensure faithful replication of deoxyribonucleic acid (DNA)—the double-helix molecule carrying an organism's genetic blueprint—before cells divide. Typically, they read an existing DNA template strand and assemble a complementary copy by linking nucleotides (the building blocks adenine [A], thymine [T], cytosine [C], and guanine [G]). However, since the 1960s, scientists have observed that some polymerases exhibit untemplated activity, adding nucleotides freely without a template. Until now, this 'doodling' was dismissed as a quirky side effect, with little insight into the sequences produced or their controllability.

Decoding the Doodling Phenomenon Through Advanced Sequencing

The Bristol team's breakthrough came from applying long-read nanopore sequencing—a cutting-edge technique that reads DNA by passing it through tiny protein pores to detect electrical changes as bases pass through—to analyze thousands of DNA molecules synthesized solely by polymerases. They tested a diverse array of natural and engineered polymerases under varied conditions, including different temperatures and nucleotide (dNTP) compositions.

Results revealed astonishing diversity: sequences ranged from simple dinucleotide repeats (e.g., ATATATA...) to complex octamer motifs, with some fragments exceeding 85,000 bases—far surpassing the few hundred bases achievable by current chemical DNA synthesis methods. Atomic force microscopy (AFM) further confirmed the physical structures, showing linear single-stranded DNA (ssDNA) polymers.

Crucially, the process proved tunable. Limiting to two dNTPs (e.g., dATP and dTTP) yielded highly regular, repetitive patterns over 1,000 bases long. Temperature tweaks shifted motif preferences, enabling 'steering' toward desired outputs. Real-time fluorescence assays tracked synthesis kinetics, highlighting how environmental factors dictate sequence emergence.

Spotlight on the Research Team at Bristol

Co-lead authors Simeon D. Castle and Thea C.T. Irvine, both PhD students in Engineering Biology at Bristol's School of Biological Sciences, drove the experimental work. Castle noted the unexpected complexity: "What we found was far more diverse and complex than anyone had appreciated—from simple two-base repeats to elaborate eight-base motifs." Irvine highlighted controllability: "By changing the temperature or limiting which DNA building blocks were available, we could shift the composition of the sequences generated."

Senior author Professor Thomas E. Gorochowski, a Royal Society University Research Fellow and head of the Biocompute Lab, integrated computational analysis. His expertise in synthetic biology and cellular computation has positioned Bristol as a UK leader in engineering biology. Collaborators included Philipp Holliger from the MRC Laboratory of Molecular Biology and teams from St Andrews and US partners Replay Holdings and the Center of Excellence for Engineering Biology.

Bristol's Biological Sciences ranks 51st globally in QS World University Rankings by Subject 2026, reflecting its prowess. The Bristol BioDesign Institute (BBI) and BrisEngBio centre underscore the university's synthetic biology ecosystem, fostering innovations from protein engineering to cellular reprogramming.

From Biological Curiosity to Biotechnology Game-Changer

Traditional DNA synthesis relies on phosphoramidite chemistry: solid-phase assembly of oligonucleotides (short DNA strands) up to ~200 bases, then enzymatic ligation for longer constructs. It's error-prone, costly (£0.10-0.20 per base), and slow for kilobase-scale DNA needed for gene therapies or genome editing.

Polymerase doodling offers an enzymatic alternative: faster, cheaper, and scalable in aqueous conditions. By engineering polymerases (via AI-directed evolution) and optimizing conditions, guided de novo synthesis could produce custom kilobase DNA directly. Applications span:

• Synthetic genomics: Building minimal genomes or viral vectors for vaccines.
• Gene therapy: Custom transgenes for CRISPR delivery.
• Biomanufacturing: Engineering microbes for biofuels or therapeutics.

The global synthetic biology market, valued at ~£21 billion in 2026, is projected to grow at 22% CAGR to £88 billion by 2033, with Europe (including UK) at 23% CAGR. UK's BrisSynBio and EPSRC/BBSRC funding amplify Bristol's impact.

Photo by Korng Sok on Unsplash

Bristol's Role in UK Synthetic Biology Leadership

The University of Bristol exemplifies UK higher education's strength in life sciences. Home to the BBI, it pioneers multidisciplinary synbio, from engineered cells for biomedicine to sustainable manufacturing. REF 2021 impact cases highlight commercial spinouts driving South West economic growth.

Gorochowski's lab complements this, blending computation with wet-lab experiments. UKRI's £13.6m BrisSynBio investment has trained cohorts via the Engineering Biology CDT, producing innovators. Amid UKRI funding pauses in physics/medicine, biology's resilience shines, with Bristol securing MRC/EPSRC grants for this work.

Evolutionary Insights: Doodling's Role in Genetic Innovation

Beyond tech, doodling may explain genetic novelty. Untemplated additions could seed mutations, repeats (implicated in diseases like Huntington's), or horizontal gene transfer. Diverse motifs suggest polymerases 'explore' sequence space, akin to AI generative models. In evolution, this might accelerate adaptation, paralleling RNA world hypotheses where polymerases bootstrapped life.

Bristol's analysis enriches this: motif enrichment (e.g., poly-A tracts) mirrors natural repeats, hinting at primordial mechanisms.

Challenges and Next Steps in Harnessing Doodling

While promising, hurdles remain: sequence fidelity (errors ~1-10%), directionality control, and integration with double-strand synthesis. AI protein design (e.g., AlphaFold3) could evolve 'designer polymerases' for specific motifs. Scaling reactors for industrial output needs bioprocess engineering.

Bristol plans iterative engineering, partnering with Replay Holdings. UK policy, via Industrial Strategy, supports via catapults like the Centre for Synthetic Biology.

Impacts on Higher Education and Careers in UK Biosciences

This discovery boosts demand for synbio expertise. Bristol's PhD programs in Engineering Biology attract top talent, with CDT placements in industry. UK unis face funding squeezes, but biology thrives—BBSRC invests £2bn annually. Careers span academia, biotech (e.g., Oxford Nanopore), and pharma.

Statistics: UK synbio jobs grew 15% YoY; PhDs earn £40k starting, rising to £80k senior.Bristol press release

Photo by Ian Cylkowski on Unsplash

Future Horizons: Revolutionizing Genomics from Bristol

Gorochowski envisions: "Harnessing doodling... could be closer than many think." Combined with CRISPR, it could enable on-demand genomes for personalized medicine or climate-resilient crops. For UK HE, Bristol exemplifies translating curiosity-driven research to global impact, inspiring the next generation.

As synbio surges, Bristol's doodling breakthrough positions UK at the forefront, promising economic and scientific dividends.