FAQ

For research-grade plasmids, we perform the QC tests listed below.

Appearance: A visual inspection of the plasmid solution to assess its clarity and the absence of particles or discoloration.
A260/280: Measures the purity of plasmid DNA by comparing absorbance at 260 nm (nucleic acids) and 280 nm (proteins). A ratio of ~1.8 indicates pure DNA.
Homogeneity by Agarose Gel: Assesses the uniformity of plasmid DNA by running it on an agarose gel to ensure consistent molecular weight and the ratio of supercoiled plasmids.
Restriction Analysis: Verifies the identity and integrity of plasmid DNA by cutting it with specific restriction enzymes and analyzing the resulting fragments via gel electrophoresis.
Endotoxin by LAL: Detects bacterial endotoxins in plasmid preparations using the Limulus Amebocyte Lysate (LAL) assay, ensuring plasmids are safe for sensitive applications.

Additionally, upon request, we offer extra QC tests, which are also included in our preclinical plasmid quality control.

Homogeneity by HPLC: Uses High-Performance Liquid Chromatography (HPLC) to evaluate the uniformity and purity of plasmid DNA, and measure the ratio of supercoiled plasmid DNA.
Residual RNA by SYBRGold: Quantifies any remaining RNA in the plasmid preparation by staining with SYBRGold and analyzing fluorescence intensity.
Residual E. coli DNA by qPCR: Detects and quantifies residual E. coli genomic DNA in plasmid preparations using quantitative PCR (qPCR).
Bioburden Testing by Direct Inoculation: Assesses the microbial contamination level of the plasmid preparation by inoculating samples in growth media and monitoring for microbial growth.
Sequencing by Sanger: Confirms the accuracy of the plasmid sequence by using Sanger sequencing to verify the inserted DNA or the entire plasmid.
Residual Host Protein by ELISA: Detects any leftover host proteins in plasmid preparations using an ELISA assay specific to E. coli proteins.
Mycoplasma Contamination by qPCR: Screens for mycoplasma contamination in the plasmid sample using sensitive qPCR techniques.
pH by Potentiometry: Measures the pH of the plasmid solution to ensure it is within the acceptable range for stability and application.
Residual Kanamycin by ELISA: Detects any remaining kanamycin antibiotic from the plasmid selection process using an ELISA assay.
Sterility: Confirms the absence of viable microorganisms in the plasmid preparation, ensuring it is sterile and suitable for sensitive applications.
Osmolality: Measures the osmolality (concentration of solutes) in the plasmid solution to ensure it is within acceptable limits for biological compatibility.

We use seamless cloning to construct most plasmids.

Seamless cloning is a method that allows precise insertion of DNA fragments into plasmid vectors without adding extra nucleotides at the junctions, a common issue with traditional restriction enzyme methods. This is crucial for protein expression, as even small additional amino acids can affect protein function. There are various approaches to seamless cloning, including techniques like overlap extension PCR or commercial kits.

Key Steps in Seamless Cloning:
Creation of Overlapping Ends: The DNA fragments are generated through PCR with ends that overlap with each other or the plasmid. These overlaps are designed into the primers used for amplification.
Annealing of Overlapping Ends: The complementary overlapping regions hybridize when mixed together.

Extension and Ligation:
A polymerase may extend the annealed fragments, filling in gaps.
DNA ligase then seals the nicks, or a commercial system may combine both enzymatic steps in a single process.

Requirements:
DNA Fragments with Overlaps: These fragments, usually created by PCR, must have complementary sequences for hybridization.
Polymerase: A polymerase is needed for filling in gaps, if required.
DNA Ligase: Ligase seals the nicks unless using a system that combines all steps.

Pros and Cons:

Pros:
Enables precise, in-frame gene insertions without unwanted nucleotides.
No need for restriction enzyme sites, giving more design flexibility.
Simplified primer design.

Cons:
Primer design requires precision for correct overlap and orientation.
Efficiency can depend on factors like fragment size and sequence complexity.
Commercial kits can be expensive.

Tips and Tricks:
Optimal Overlap Length: Overlaps of 15–25 nucleotides typically provide efficient annealing, though larger fragments may require longer overlaps.
High Purity DNA: DNA fragments should be pure, often achieved by gel purification post-PCR, for optimal results.
Control Reactions: Always include controls (like no-insert controls) to detect potential background noise or unwanted ligation.

We use the strains below depend on different applications:

1. DH5α
Genotype: F–, φ80dlacZΔM15, Δ(lacZYA-argF)U169, recA1, endA1, hsdR17(rK–, mK+), phoA, supE44, λ–, thi-1, gyrA96, relA1
Applications: Commonly used for general cloning purposes and blue/white screening. Its mutations in recA and endA enhance plasmid stability and transformation efficiency, making it a go-to strain for many cloning applications.

2. Top10
Genotype: F–, mcrA, Δ(mrr-hsdRMS-mcrBC), φ80lacZΔM15, ΔlacX74, recA1, araD139, Δ(ara-leu)7697, galU, galK, λ–, rpsL(StrR), endA1, nupG
Applications: Suitable for general cloning and blue/white screening with high transformation efficiency. It is often preferred when maximizing the number of transformants is critical.

3. Stbl3
Genotype: F–, mcrB, mrr, hsdS20(rB–, mB–), recA13, supE44, ara-14, galK2, lacY1, proA2, rpsL20(StrR), xyl-5, λ–, leu, mtl-1
Applications: Ideal for cloning vectors with repetitive elements, such as long terminal repeats (LTRs) in lentiviral plasmids. The recA mutation minimizes recombination, enhancing the stability of complex constructs.

4. XL-10
Genotype: TetR Δ(mcrA)183 Δ(mcrCB-hsdSMR-mrr)173 endA1 supE44 thi-1 recA1 gyrA96 relA1 lac Hte [F´ proAB lacIqZΔM15 Tn10 (TetR) Amy CamR]
Applications: Optimized for high-efficiency transformation, particularly for large or methylated DNA constructs. It is also suitable for blue/white screening and for cloning unstable or toxic sequences due to the recA mutation.

5. NEB Stable
Genotype: F´ proA+B+ lacIq Δ(lacZ)M15 Tn10 (TetR) endA1 recA1 hsdR17(rK– mK+) glnV44 λ– thi-1 gyrA96 relA1 spoT1
Applications: Designed to maintain unstable plasmids that might recombine or degrade in other strains. It is ideal for cloning large or recombination-prone plasmids, offering good yield and stability for long-term propagation.

An Antibiotic Resistance Gene in a plasmid provides the host cell with the ability to survive in the presence of a specific antibiotic. This is used as a selection marker to ensure that only cells that have successfully taken up the plasmid (transformed cells) will grow in an antibiotic-containing environment. Common antibiotic resistance genes include AmpR (confers resistance to ampicillin) and KanR (confers resistance to kanamycin). Researchers use antibiotic selection to isolate and maintain populations of cells containing the plasmid.

The Polyadenylation Signal (Poly(A)) is a sequence found near the end of a gene that directs the addition of a poly(A) tail to the mRNA during transcription. This poly(A) tail plays a vital role in stabilizing mRNA and enhancing its translation into proteins. It also aids in mRNA export from the nucleus to the cytoplasm. Including a poly(A) signal in a plasmid ensures that the mRNA produced from the gene of interest will be properly processed, resulting in more stable and efficiently translated transcripts.

Regulatory elements are sequences within the plasmid that help control the expression of the gene of interest. One common regulatory element is the Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element (WPRE), which enhances the stability and translation efficiency of mRNA. WPRE is often included in viral vectors or plasmids to increase gene expression, leading to higher levels of protein production in the host cells. Other regulatory elements may control transcription rates, splicing, or mRNA transport.

An Open Reading Frame (ORF) is a continuous sequence of codons in DNA that starts with a start codon (usually AUG) and ends with a stop codon (such as UAA, UAG, or UGA). The ORF represents the portion of a gene that is translated into a protein. In plasmid design, the ORF usually includes the gene of interest that researchers wish to express in a host organism. Proper expression of the ORF is crucial for the successful production of the encoded protein.

The Multiple Cloning Site (MCS), also known as a polylinker, is a short segment of DNA that contains several unique restriction enzyme recognition sites. These sites allow researchers to insert a gene of interest into the plasmid at a specific location. The MCS simplifies the process of cloning because it offers flexibility in choosing which restriction enzymes to use, making it easier to incorporate foreign DNA fragments into the plasmid without disrupting other essential elements.

Today, seamless cloning methods are often preferred over using restriction enzymes in the MCS for gene insertion. However, the restriction enzyme sites within the MCS still provide a convenient location for plasmid linearization during seamless cloning.