Plasmid: A Small Circular DNA Molecule with Big Potential

Plasmids, small circular DNA molecules, serve as essential vectors for DNA recombination in molecular biology research and gene therapy. The yield and quality of plasmids are crucial, with supercoiled proportion and endotoxin content being two significant factors affecting plasmid quality.

Plasmid Subtypes

Plasmids extracted from Escherichia coli (E. coli) exist in various subtypes: supercoiled (SC), open circular (OC), and linear (L) forms (Figure 1). Among them, supercoiled plasmids exhibit excellent stability, antigenicity, and high transfection and expression efficiency.

Figure 1. Schematic Diagram of Common Plasmid Subtypes

In agarose gel electrophoresis of plasmid DNA, the order of migration speed is supercoiled DNA, linear DNA, and open circular DNA (Figure 2).

Figure 2. Agarose Gel Electrophoresis Migration Pattern of Different Plasmid Subtypes

Yaohai Bio-Pharma has continuously improved its processes and techniques to ensure that the supercoiled proportion of transfection-grade plasmids is ≥85% and that of research-grade plasmids is ≥50%. The following is a case demonstration (Figure 3), where agarose gel electrophoresis is combined with Gel-Pro Analyzer software to detect the supercoiled proportion.

Figure 3. Quality Inspection Results of Plasmid Supercoiled Proportion

Endotoxin

Endotoxin, a component of the cell wall of Gram-negative bacteria, primarily consists of lipopolysaccharide A (LPS-A) as its toxic component. During plasmid extraction, endotoxin is released into the lysis solution, severely affecting the efficiency of plasmid transfection into cells. Additionally, it can activate non-specific immune responses in cells, leading to false positives in experiments.

Yaohai Bio-Pharma adopts a "non-introduction" and "high removal" approach, strictly controlling the use of reagents and materials containing endotoxin throughout the purification process. The company has also developed an efficient endotoxin removal method, offering three levels of endotoxin content: ≤0.1 EU/µg, ≤0.01 EU/µg, and ≤0.005 EU/µg.

Yaohai Bio-Pharma possesses a high-throughput plasmid extraction service line, capable of delivering 1 mg of extracted plasmids in as fast as one week. By default, it provides more than seven quality control (QC) tests to ensure the delivery of high-quality, high-standard plasmids from multiple perspectives.

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