Key Takeaways & Executive Findings
- •• A novel cloning method eliminates the need for PCR and annealing steps, using a single oligo for short DNA fragment insertion. • The method leverages host cell DNA polymerase for complementary strand synthesis, with T4 DNA polymerase supplementation enhancing efficiency. • Cloning time is reduced to under 1 hour, significantly faster than traditional methods requiring 2+ hours. • The technique is broadly applicable for cloning shRNA and sgRNA, streamlining gene knockdown and CRISPR/Cas9 genome editing workflows.
Abstract
Cloning short DNA fragments, such as shRNA and sgRNA, is a routine but time-consuming task in molecular biology. Traditional methods require annealing of complementary oligos or PCR amplification, which are labor-intensive and time-consuming. Here, we report a novel PCR-independent, annealing-free cloning method that enables the insertion of short DNA fragments using a single oligo. The method relies on T4 DNA ligase for ligation and host cell DNA polymerase for complementary strand synthesis. We demonstrate that adding T4 DNA polymerase and dNTPs to the ligation mixture significantly improves cloning efficiency. This approach simplifies the cloning process, reduces time to less than 1 hour, and is compatible with standard laboratory reagents. Our method provides a rapid and efficient alternative for cloning short DNA fragments, with broad applications in gene knockdown and genome editing.
1. Introduction
Since two major biotechnological advances, the discovery of restriction endonucleases in the 1970s [1] and the invention of the polymerase chain reaction (PCR) technique in the 1980s [2], molecular cloning has become a fundamental laboratory technique in life sciences and biomedical research. This technique allows the generation of recombinant DNA molecules from selected DNA fragments and has become an extremely powerful tool for DNA manipulation [3]. Traditionally, molecular cloning involves joining linearized vectors and DNA fragments, which may have blunt ends or complementary sticky ends generated by restriction enzymes or by annealing single-stranded oligonucleotides (oligos), using T4 DNA ligase [4]. The traditional cloning procedure involves multiple steps, such as DNA purification, endonuclease digestion or annealing of single-stranded oligos, ligation, and transformation, all of which can be time-consuming.
To simplify the classical molecular cloning process and increase cloning efficiency, scientists have developed several alternative cloning approaches, including endonuclease-independent TOPO cloning, ligation-independent T4 DNA polymerase cloning, overlap extension PCR cloning, recombination-mediated Gateway cloning, and Gibson assembly. Each method offers distinct advantages and is tailored to specific cloning needs, providing valuable tools for genetic engineering and molecular biology research [5‒7]. Although these methods significantly improve the efficiency of cloning relatively long DNA constructs, cloning short DNA fragments remains a time-consuming and challenging task. This underscores the critical need for innovative approaches that could specifically improve the efficiency and reduce the time required for cloning short DNA fragments.
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Linbo Li, Jin Yan, Yuan Qi, Zhenglong Xiang, Na Jiang, Tongkang Yuan, Zhenyi Wang, Yuan Wang, Huaizhe Zhan, Shiyi Liu, Li Zhao, Jing Xu, Xiaowei Lei, Yuxuan Liu, Gui Wang, Jiayang Xie, Zhenming Guo, Chunhai Cai, Shan Bian (2026). A PCR-independent, annealing-free cloning method for the insertion of short DNA fragments. Acta Biochimica et Biophysica Sinica. https://doi.org/10.3724/abbs.2024088
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Frequently Asked Questions
What is the main advantage of this new cloning method?
The method eliminates the need for PCR and annealing steps, allowing insertion of short DNA fragments using a single oligo, reducing cloning time to under 1 hour.
How does the method work?
A single oligo is ligated into a linearized vector using T4 DNA ligase, and the complementary strand is synthesized by host cell DNA polymerase after transformation. Adding T4 DNA polymerase and dNTPs to the ligation mixture enhances efficiency.
What types of DNA fragments can be cloned with this method?
It is suitable for short DNA fragments such as shRNA and sgRNA, commonly used for gene knockdown and CRISPR/Cas9 genome editing.
Is the method compatible with standard laboratory reagents?
Yes, it uses standard reagents like T4 DNA ligase, T4 DNA polymerase, and dNTPs, and the buffers are compatible, retaining 75-100% activity.
How does this method compare to traditional cloning in terms of time?
Traditional methods require annealing or PCR steps that take over 2 hours, while this method can be completed in less than 1 hour, significantly saving time.
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