One Plasmid, One Week, One Revolution: How T7-ORACLE Rewrites Protein Evolution

Background

No complex instruments. No repetitive manipulation. Just one plasmid—and your target gene can undergo continuous hypermutation inside living cells, enhancing protein activity by thousands of times within a week!

It may sound like a synthetic biologist’s dream, but it has now become reality. On August 7, 2025, Peter Schultz’s team at the Scripps Research Institute published a groundbreaking study in Science, unveiling a system called T7-ORACLE, an orthogonal replication system that enables continuous, rapid, and targeted gene hypermutation in E. coli. This represents a revolutionary breakthrough in protein-directed evolution.

Directed protein evolution has generated next-generation T7 RNA polymerase variants with 50% higher yield and 90% reduced dsRNA contamination. These engineered enzymes enable cost-effective mRNA manufacturing for vaccines and therapeutics.

Bottlenecks in Traditional Evolution Technologies

Directed evolution is a key strategy for optimizing protein function, yet traditional approaches such as error-prone PCR or DNA shuffling have significant limitations: they rely on multiple rounds of in vitro mutation–transformation–screening cycles, which are labor-intensive and time-consuming, and they often fail to achieve deep evolutionary changes.

Although recent in vivo evolution technologies (like PACE) have improved efficiency, they still face issues such as non-targeted mutations, host genome instability, and the need for specialized equipment.

Inspired by bacteriophage T7, the Schultz team developed a fully orthogonal replication system composed of multiple components: T7 replicative proteins, including RNA polymerase, DNA polymerase, helicase–primase fusion protein, and single-stranded DNA-binding protein.

Mechanism:

The system works by expressing T7 RNA polymerase, DNA polymerase, helicase–primase, and single-stranded binding protein, which specifically recognize and replicate circular target plasmids carrying the T7 replication origin.

To promote replication, a catalytically defective T7 lysozyme is fused to the T7 RNA polymerase. The inhibitory effect of T7 lysozyme prevents full transcription, generating short RNA primers that initiate replication by T7 DNA polymerase.

By introducing engineered T7 DNA polymerase variants (Δ28 deletion and key mutations N520M, P560V, and V443K), the fidelity of replication is drastically reduced.

Figure 1. Schematic diagram of the directed evolution workflow

T7-ORACLE: A Precise “Genetic Editing Engine”

The Schultz team designed the T7-ORACLE system as a fully orthogonal replication mechanism inspired by bacteriophage T7.

It consists of several key components: T7 RNA polymerase, DNA polymerase, helicase–primase fusion protein, and single-stranded binding protein.

The system specifically targets plasmids carrying the T7 replication origin (φOR) for replication.

Figure 2. Life cycle of T7 bacteriophage

Class I genes encode host-suppression functions and T7 RNA polymerase;

Class II genes encode the T7 replication machinery;

Class III genes encode T7 capsid and lysis proteins.

Figure 3. Schematic diagram of system design principle

To maximize mutational efficiency, the engineered DNA polymerase exhibits reduced proofreading activity and base selectivity, resulting in controlled hypermutation.

Most importantly, this system targets only the plasmid-borne genes without disturbing the host genome, allowing E. coli cells to maintain normal growth while achieving extremely high mutation rates in the target sequence.

How Is a Million-Fold Increase in Mutation Rate Achieved?

The researchers used rational design and directed evolution to iteratively optimize T7 DNA polymerase:

Removing proofreading activity:

An exonuclease-deficient mutant (Δ28) raised the mutation rate 25-fold.

Reducing base-pairing fidelity:

Key mutations N520M, P560V, and V443K further lowered replication accuracy.

Figure 4. Engineered T7 DNA polymerases involved in this study

The resulting five-mutation polymerase achieved a mutation rate of 1.7×10⁻⁵ per base per generation, nearly 100,000 times higher than the host genome mutation rate, while maintaining high transformation efficiency (2.4×10¹⁰ cfu/μg).

Stability tests of the optimized system included:

Fluctuation analysis,

confirming excellent orthogonality (genomic mutation rate 4.4×10⁻¹⁰ spb);

Sequencing of mutation spectra,

showing unbiased substitution patterns (balanced transition/transversion rates);

Serial passage experiments,

confirming plasmid stability and negligible metabolic burden for plasmids up to 13 kb

Figure 5. Stability testing of the optimized system

Application: Hyperactive β-Lactamase Evolved in Just One Week

To validate the system’s practicality, the team applied it to evolve TEM-1 β-lactamase.

In less than one week, mutants exhibiting 5,000-fold higher resistance to several clinically important antibiotics (aztreonam, cefotaxime, ceftazidime, and cefepime) were obtained.

Remarkably, the mutations that emerged (such as G238S, R164H, and E104K) were identical to those observed in clinical antibiotic-resistant strains, proving that the system accurately mimics natural evolutionary processes.

Figure 6. Continuous evolution of β-lactamase

Breaking Local Optima: From a Single Starting Point to Global Library Evolution

One of T7-ORACLE’s major advantages is its compatibility with pre-constructed mutation libraries.

The researchers compared different evolutionary starting points:

From the wild-type sequence

– the evolution pathway was highly convergent (single-directional evolution).

From single-point saturation mutants

– multiple unidirectional trajectories emerged.

From a full saturation library

– multiple multidirectional trajectories were observed, enabling exploration of the global fitness landscape and identification of global optima.

Figure 7. Exploring broader fitness landscapes from multiple starting points toward whole-library evolution

Technological Prospects and Significance

Key advantages of this work include:

Development of a hypermutation system combining strong target specificity, safety, and long mutational reach

— maintaining host genome stability while enabling evolution of any target protein length.

Accelerating protein functional evolution and overcoming local fitness peaks

— by integrating pre-diversified mutation libraries to shift from directed evolution to global adaptive landscape exploration.

However, questions remain regarding whether the mutation distribution along target genes is fully uniform, and whether bias toward promoter-proximal regions occurs.

Note:

This study was published in Science on August 7, 2025, under the title:
“An orthogonal T7 replisome for continuous hypermutation and accelerated evolution in E. coli.”

Original article link:

https://www.science.org/doi/10.1126/science.adp9583

Product Recommendation

GMP-Grade T7 RNA Polymerase

During in vitro transcription, T 7 RNA polymerase binds to the T7 promoter sequence in the DNA template to amplify a large amount of mRNA. Hzymes Biotech provides wild-type and more than 30 engineered T7 RNA polymerase mutants to meet the needs of different application scenarios.