# cDNA Library Construction: Steps, Applications, and Pitfalls

## Introduction to cDNA Libraries

### What is a cDNA Library?

A cDNA library is a collection of cloned complementary DNA (cDNA) fragments derived from the messenger RNA (mRNA) population of a particular cell or tissue type at a specific developmental stage or physiological condition. The term "library" refers to the fact that the collection contains representatives of all the expressed genes in the source material, each inserted into a vector molecule that can be propagated in a host organism, typically *Escherichia coli*.

The construction of a cDNA library begins with the conversion of mRNA into double-stranded DNA using the enzyme reverse transcriptase. This enzyme, originally discovered in retroviruses, catalyzes the synthesis of DNA from an RNA template. The resulting cDNA molecules lack introns, promoter sequences, and other regulatory elements found in genomic DNA because they are direct copies of processed, mature mRNA transcripts.

cDNA libraries are fundamentally different from genomic libraries in both their composition and their utility. A genomic library contains fragments of total genomic DNA, including introns, intergenic regions, regulatory sequences, and repetitive elements. A cDNA library, by contrast, contains only the sequences that are actually transcribed into mRNA and translated into protein. This makes cDNA libraries the tool of choice when the goal is to study gene expression, isolate coding sequences, or produce recombinant proteins.

### cDNA vs. Genomic Library

The distinction between cDNA and genomic libraries is one of the most important conceptual points in [molecular cloning](/knowledge/molecular-biology/molecular-cloning-a-laboratory-manual). The table below summarizes the key differences.

| Feature | cDNA Library | Genomic Library |
|---------|--------------|-----------------|
| Source material | mRNA (processed transcripts) | Total genomic DNA |
| Contains introns | No | Yes |
| Contains regulatory sequences | No | Yes (promoters, enhancers) |
| Contains repetitive DNA | No | Yes |
| Representation | Only expressed genes | All genes, expressed or not |
| Gene size representation | Full-length transcripts possible | Large genes may be fragmented |
| Typical use | Gene cloning, expression studies | Genome mapping, sequencing, promoter analysis |

The choice between a cDNA and genomic library depends entirely on the experimental question. If you want to study the coding sequence of a gene, determine what proteins a cell produces, or express a eukaryotic gene in bacteria, a cDNA library is appropriate. If you want to study gene structure, regulatory elements, or the organization of a genome, a genomic library is required.

## The Principle Behind cDNA Synthesis

### From mRNA to cDNA

[The central dogma of molecular biology](/blog/news/the-central-dogma-of-molecular-biology) describes the flow of genetic information: DNA is transcribed into RNA, and RNA is translated into protein. In eukaryotic cells, the primary transcript (pre-mRNA) undergoes extensive processing before it becomes mature mRNA. This processing includes the addition of a 5′ cap, the removal of introns through splicing, and the addition of a poly(A) tail at the 3′ end. The mature mRNA that exits the nucleus is therefore a processed, protein-coding template.

cDNA synthesis reverses this flow at the molecular level. Using mRNA as a template, reverse transcriptase generates a single-stranded DNA molecule that is complementary to the mRNA. This first-strand cDNA is then converted into double-stranded DNA, which can be ligated into a vector and cloned. The resulting cDNA sequence corresponds exactly to the coding sequence of the gene, minus the introns.

The key advantage of using mRNA as the starting material is that it provides a snapshot of gene expression. Only genes that are actively transcribed in the source tissue will be represented in the library. This is particularly valuable when comparing gene expression between different cell types, developmental stages, or disease states.

### Role of Reverse Transcriptase

Reverse transcriptase (RT) is an RNA-dependent DNA polymerase that was first discovered in retroviruses, where it converts the viral RNA genome into DNA for integration into the host genome. The two most commonly used reverse transcriptases in [molecular biology](/blog/careers/molecular-biology) are:

- **Moloney Murine Leukemia Virus (M-MLV) reverse transcriptase**: A single-subunit enzyme with relatively low RNase H activity. It operates optimally at 37–42°C and produces cDNAs up to approximately 7–8 kb in length.
- **Avian Myeloblastosis Virus (AMV) reverse transcriptase**: A two-subunit enzyme with higher RNase H activity. It is more thermostable than M-MLV RT and can operate at up to 50°C, which helps reduce secondary structure in RNA templates.

The RNase H activity of reverse transcriptase is important to understand. RNase H degrades the RNA strand in an RNA–DNA hybrid. During first-strand synthesis, this activity can degrade the mRNA template while it is being copied, leading to truncated cDNAs. For this reason, engineered versions of M-MLV RT with reduced or abolished RNase H activity (such as SuperScript II and SuperScript III) are often preferred for full-length cDNA synthesis.

Reverse transcriptase requires a primer with a free 3′ hydroxyl group to initiate synthesis. For cDNA library construction, the primer is typically an oligo(dT) primer that anneals to the poly(A) tail of eukaryotic mRNA. Alternatively, random hexamer primers can be used to prime synthesis from internal sites within the mRNA, which is useful for capturing sequences that are far from the 3′ end or for RNA molecules that lack a poly(A) tail.

## Steps in cDNA Library Construction

The construction of a cDNA library is a multi-step procedure that requires careful attention to RNA quality, enzyme activity, and cloning efficiency. The following is a step-by-step outline of the process.

### mRNA Isolation

The first and most critical step is the isolation of high-quality mRNA. Total RNA is typically extracted from cells or tissues using guanidinium thiocyanate-phenol-chloroform extraction (e.g., TRIzol reagent) or silica column-based kits. The integrity of the RNA must be verified, usually by agarose gel electrophoresis or microfluidic analysis, to ensure that the ribosomal RNA bands are intact and that there is no degradation.

Since mRNA constitutes only 1–5% of total RNA, it must be purified from the abundant ribosomal RNA (rRNA) and transfer RNA (tRNA). This is almost always accomplished using oligo(dT) affinity chromatography. The total RNA is passed over a column containing oligo(dT) cellulose or magnetic beads coated with oligo(dT). The poly(A) tails of mRNA hybridize to the oligo(dT), while rRNA and tRNA, which lack poly(A) tails, flow through. The mRNA is then eluted by lowering the salt concentration and raising the temperature.

The quality of the mRNA is paramount. Degraded mRNA will produce truncated cDNAs and a library that is not representative of the true transcriptome. The presence of contaminating genomic DNA must also be avoided, as it will be cloned along with the cDNA and produce false positives.

### First-Strand Synthesis

First-strand cDNA synthesis is the conversion of mRNA into single-stranded cDNA. The reaction typically contains:

- 1–5 μg of purified mRNA
- Oligo(dT) primer (e.g., 0.5 μg per reaction) or random hexamers
- dNTPs (0.5 mM each)
- Reverse transcriptase (200 units of M-MLV RT or equivalent)
- Reaction buffer (50 mM Tris-HCl, pH 8.3, 75 mM KCl, 3 mM MgCl₂)
- DTT (5–10 mM) to stabilize the enzyme
- RNase inhibitor (e.g., RNasin) to protect the RNA from degradation

The reaction is incubated at 42°C for 60 minutes. If the mRNA has significant secondary structure, a higher temperature (50°C) with a thermostable RT such as SuperScript III may be used.

The oligo(dT) primer anneals to the poly(A) tail, and reverse transcriptase extends from the 3′ end of the primer, synthesizing a cDNA strand complementary to the mRNA. The result is an mRNA–cDNA hybrid molecule.

### Second-Strand Synthesis

The second strand is synthesized by one of several methods. The classic method exploits the fact that the first-strand cDNA often has a short hairpin loop at its 3′ end, formed by the reverse transcriptase turning back on itself. This hairpin can prime second-strand synthesis.

In the RNase H method, which is more commonly used today:

1. The mRNA–cDNA hybrid is treated with RNase H, which nicks the RNA strand at multiple sites, leaving short RNA fragments that serve as primers.
2. DNA polymerase I (holoenzyme) is added. It extends from the 3′ ends of the RNA primers, synthesizing the second DNA strand. The 5′→3′ exonuclease activity of DNA polymerase I removes the RNA primers as it proceeds.
3. The remaining RNA fragments are removed, and the single-stranded nick between the Okazaki-like fragments is sealed by DNA ligase.

The result is a double-stranded cDNA molecule with a sequence identical to the original mRNA (with T substituted for U). The double-stranded cDNA is then treated with S1 nuclease to remove the hairpin loop, although this step is often omitted in modern protocols that use the RNase H method.

### Ligation into Vector

The double-stranded cDNA must be inserted into a vector for propagation. Several strategies exist:

**Linker/Adapter Ligation**: The cDNA ends are blunted using T4 DNA polymerase or the Klenow fragment. Phosphorylated linkers or adapters containing restriction sites (e.g., *Eco*RI) are ligated to the blunt ends using T4 DNA ligase. The linkers are then digested with the appropriate restriction enzyme to generate cohesive ends. The cDNA is then ligated into a vector that has been digested with the same enzyme.

**Directional Cloning**: To ensure that the cDNA is inserted in the correct orientation relative to a promoter, adapters with different restriction sites are ligated to the 5′ and 3′ ends. For example, a *Sal*I adapter is ligated to the 5′ end and a *Not*I adapter to the 3′ end. The cDNA is then ligated into a vector digested with *Sal*I and *Not*I, ensuring that the cDNA is oriented with its 5′ end near the vector's promoter. This is essential for [expression vector](/knowledge/molecular-biology/expression-vector) construction.

**TA Cloning**: If the cDNA was synthesized using a polymerase that adds a single 3′ A overhang (as is common in PCR-based methods), the cDNA can be ligated directly into a T-vector that has a complementary 3′ T overhang.

The choice of vector depends on the downstream application. Plasmid vectors are suitable for most purposes, while bacteriophage λ vectors (e.g., λgt11) were historically used for larger libraries because of their higher cloning efficiency. Phagemid vectors combine features of both.

### Transformation and Amplification

The ligated cDNA–vector molecules are introduced into competent *E. coli* cells by heat shock or electroporation. The efficiency of [transformation bacteria](/knowledge/molecular-biology/transformation-bacteria) is a major determinant of library size. A typical cDNA library should contain at least 10⁵–10⁶ independent clones to ensure that rare transcripts are represented.

After transformation, the cells are plated on selective medium (e.g., ampicillin or kanamycin) to select for cells that have taken up the vector. The resulting colonies or plaques constitute the primary library. This primary library can be amplified by scraping all colonies from the plate and replating them at a higher density, creating a stable stock that can be screened multiple times.

## cDNA Library Diagram and Visual Overview

### Key Components in a Diagram

A typical diagram of cDNA library construction would show the following steps in sequence:

1. **mRNA with poly(A) tail**: A line with a series of A's at the 3′ end, representing the poly(A) tail.
2. **Oligo(dT) primer annealing**: A short sequence of T's hydrogen-bonded to the poly(A) tail.
3. **First-strand synthesis**: An arrow showing reverse transcriptase extending from the primer, with a dashed line representing the newly synthesized cDNA.
4. **RNA removal and second-strand synthesis**: RNase H nicking the RNA, followed by DNA polymerase I synthesizing the second strand.
5. **Double-stranded cDNA**: Two parallel lines representing the completed cDNA.
6. **Adapter ligation**: Short sequences added to the ends of the cDNA.
7. **Vector ligation**: The cDNA inserted into a circular plasmid vector.
8. **Transformation**: The recombinant plasmid entering an *E. coli* cell.

When reading such a diagram, pay attention to the orientation of the cDNA relative to the vector's promoter and the restriction sites used for cloning. These details determine whether the library can be used for expression studies.

## Types of cDNA Libraries

### Normalized cDNA Libraries

A normalized cDNA library is one in which the relative abundance of each clone has been equalized. In a standard cDNA library, highly expressed genes (e.g., housekeeping genes like actin or GAPDH) are overrepresented, while rare transcripts are underrepresented. This makes it difficult to find clones of low-abundance genes.

Normalization is achieved by denaturing the cDNA and allowing it to reanneal. Highly abundant sequences reanneal faster than rare sequences because of the higher concentration of complementary strands. The double-stranded fraction (representing abundant sequences) is then removed, typically by hydroxyapatite chromatography or by digestion with a nuclease that specifically degrades double-stranded DNA. The remaining single-stranded fraction is enriched for rare sequences and is used to construct the library.

Normalized libraries are particularly useful for large-scale gene discovery projects, where the goal is to identify as many unique genes as possible.

### Subtracted cDNA Libraries

Subtracted (or subtractive) cDNA libraries are designed to isolate genes that are differentially expressed between two cell populations. The technique involves hybridizing cDNA from one population (the "tester") with an excess of mRNA or cDNA from another population (the "driver"). Sequences common to both populations form hybrids and are removed. The remaining single-stranded cDNA represents genes that are specifically expressed in the tester population.

For example, to identify genes upregulated in cancer cells, cDNA from tumor cells (tester) is hybridized with mRNA from normal cells (driver). The unhybridized cDNA represents tumor-specific transcripts. This approach has been used to identify numerous oncogenes and tumor markers.

### Full-Length cDNA Libraries

Full-length cDNA libraries contain clones that represent the complete coding sequence of each gene, from the 5′ untranslated region to the poly(A) tail. Constructing such libraries is technically challenging because reverse transcriptase often stops prematurely due to secondary structure in the mRNA, producing truncated cDNAs that lack the 5′ end.

Several methods have been developed to enrich for full-length cDNAs:

- **Cap-trapping**: The 5′ cap structure of mRNA is biotinylated, and the mRNA–cDNA hybrid is captured on streptavidin beads. Only cDNAs that have been extended all the way to the 5′ cap are retained.
- **Oligo-capping**: The 5′ cap is replaced with a synthetic RNA oligonucleotide, which then serves as a priming site for PCR amplification of full-length cDNAs.
- **Template-switching**: The terminal transferase activity of reverse transcriptase adds a few non-templated C residues to the 3′ end of the first-strand cDNA. An oligo(dG) primer then anneals to this tail and serves as a template for extension, incorporating a known sequence at the 5′ end.

Full-length libraries are essential for functional studies, as truncated clones may lack critical N-terminal domains.

## Applications of cDNA Libraries

### Gene Cloning and Discovery

The most fundamental application of cDNA libraries is the isolation and cloning of specific genes. Before the advent of high-throughput sequencing, cDNA libraries were the primary means of identifying novel genes. Even today, cDNA libraries are used to clone genes from organisms with unsequenced genomes or to obtain full-length coding sequences for functional studies.

The classic example is the cloning of the human insulin gene. mRNA was isolated from pancreatic β-cells, converted to cDNA, and cloned into a plasmid. The insulin cDNA was then identified by hybridization screening and expressed in *E. coli* to produce recombinant human insulin.

### Studying Gene Expression

cDNA libraries provide a snapshot of gene expression in a particular tissue or cell type. By comparing libraries constructed from different samples, researchers can identify genes that are upregulated or downregulated under specific conditions. This approach has been used to study:

- Developmental changes in gene expression
- Response to environmental stress
- Differences between normal and diseased tissues
- Tissue-specific gene expression patterns

While modern RNA-seq has largely replaced cDNA libraries for global expression profiling, libraries remain valuable for validating expression data and for isolating full-length clones of differentially expressed genes.

### Construction of Expression Libraries

When cDNA is cloned into an [expression vector](/knowledge/molecular-biology/expression-vector) in the correct orientation and reading frame, the library can be screened for functional proteins. This is the basis of expression cloning, where a cDNA library is introduced into host cells and screened for a specific phenotype or activity.

For example, a cDNA library from human liver cells can be cloned into a mammalian [expression vector](/knowledge/molecular-biology/expression-vector) and introduced into cultured cells. The cells are then screened for the production of a specific protein, such as a cytokine or a receptor, using an antibody or a functional assay. The cDNA responsible for the activity can then be recovered and characterized.

Expression libraries are also used for protein production. A cDNA encoding a protein of interest can be cloned into an expression vector with a strong promoter (e.g., T7 or lac) and an affinity tag (e.g., His-tag or GST), allowing high-level production and purification of the recombinant protein.

## Screening a cDNA Library

Screening is the process of identifying the clone of interest within a library of thousands or millions of clones. Several methods are available, depending on the nature of the target.

### Hybridization Screening

Hybridization screening is the most direct method and requires a nucleic acid probe. The library is plated on agar plates at a density that produces individual colonies or plaques. A replica of the plate is made by pressing a nitrocellulose or nylon membrane onto the surface, transferring a small amount of each colony to the membrane. The membrane is then processed to denature the DNA and fix it in place.

The membrane is incubated with a labeled probe—either a radioactive (³²P-labeled) or non-radioactive (biotin- or digoxigenin-labeled) DNA or RNA fragment that is complementary to the target sequence. After hybridization and washing to remove non-specifically bound probe, the membrane is exposed to X-ray film or developed with a colorimetric or chemiluminescent substrate. Positive signals are aligned with the original plate to identify the corresponding colony, which is then picked and purified.

The probe can be a known gene fragment, an oligonucleotide designed from a conserved protein sequence, or a PCR product amplified from related species.

### Immunoscreening

Immunoscreening is used when the target is a protein and an antibody is available. This method requires an expression library in which the cDNA is cloned downstream of a promoter that is active in the host (e.g., the lacZ promoter in λgt11). The library is plated, and protein expression is induced. The proteins are transferred to a membrane, and the membrane is incubated with a primary antibody specific to the target protein. After washing, a secondary antibody conjugated to an enzyme (e.g., [alkaline phosphatase](/knowledge/molecular-biology/alkaline-phosphatase) or horseradish peroxidase) is added. The enzyme catalyzes a colorimetric reaction, producing a colored spot at the location of the positive clone.

Immunoscreening is powerful because it directly identifies clones that produce the protein of interest, regardless of the [nucleotide sequence](/knowledge/molecular-biology/nucleotide-sequence).

### Functional Screening

Functional screening relies on the biological activity of the protein encoded by the cDNA. This approach is used when no sequence information or antibody is available. The library is introduced into host cells, and the cells are screened for a specific phenotype.

For example, to clone a gene that confers resistance to a drug, a cDNA library is introduced into cells, and the cells are grown in the presence of the drug. Only cells that have taken up and expressed the resistance gene will survive. The cDNA from these surviving cells is then recovered and characterized.

Functional screening can also be used to identify genes that induce a specific morphological change, activate a reporter gene, or complement a mutation in yeast or bacteria.

## Common Pitfalls and Troubleshooting

### [mRNA Degradation](/knowledge/molecular-biology/mrna-degradation)

The most common cause of failure in cDNA library construction is the use of degraded mRNA. RNA is highly susceptible to degradation by RNases, which are ubiquitous in the environment and on human skin. Even brief exposure to RNase contamination can destroy the mRNA and produce a library of truncated cDNAs.

**Prevention**: Use RNase-free reagents and plasticware. Treat all solutions with diethyl pyrocarbonate (DEPC) or use commercially available RNase-free water. Add an RNase inhibitor (e.g., RNasin) to all reactions. Work quickly and keep RNA on ice. Always verify RNA integrity by gel electrophoresis before proceeding.

### Incomplete cDNA Synthesis

Reverse transcriptase can prematurely terminate, especially at regions of strong secondary structure in the mRNA. This produces truncated cDNAs that lack the 5′ end of the gene. The problem is exacerbated when the mRNA is long or GC-rich.

**Troubleshooting**: Use a thermostable reverse transcriptase (e.g., SuperScript III) and incubate at a higher temperature (50–55°C) to melt secondary structure. Add betaine (1–2 M) or DMSO (5–10%) to the reaction to reduce secondary structure. Alternatively, use random hexamers in addition to oligo(dT) to prime synthesis from multiple sites along the mRNA.

### Chimeric Clones

Chimeric clones are recombinant molecules in which two or more unrelated cDNA fragments are ligated together. This can occur during the ligation step, especially if the cDNA ends are not properly blunted or if the linkers are not completely digested. Chimeric clones produce misleading sequence data and must be avoided.

**Prevention**: Ensure complete digestion of linkers with restriction enzymes. Size-fractionate the cDNA before ligation to remove small fragments that are more likely to ligate to each other. Use a high molar ratio of vector to insert to favor single-insert ligation events.

### Low Representation of Rare Transcripts

In a standard cDNA library, highly abundant transcripts dominate, and rare transcripts may be absent or present at very low frequency. This is a particular problem when trying to clone genes that are expressed at low levels.

**Solutions**: Use a normalized library to equalize transcript abundance. Use a subtracted library to enrich for differentially expressed genes. Increase the size of the library by performing more transformations. Alternatively, use PCR-based amplification of the cDNA to increase the representation of rare transcripts, although this can introduce bias.

## Summary and Key Takeaways

cDNA libraries are collections of cloned DNA sequences derived from the mRNA of a cell or tissue. They provide a direct link between gene expression and gene sequence, making them indispensable tools for gene discovery, expression analysis, and protein production. The construction of a cDNA library involves mRNA isolation, first- and second-strand cDNA synthesis, ligation into a vector, and transformation into a host organism. Various specialized libraries—normalized, subtracted, and full-length—address specific experimental needs. Screening methods, including hybridization, immunodetection, and functional assays, allow the isolation of specific clones of interest.

The key points to remember are:

- cDNA libraries represent the expressed genes of a cell, not the entire genome.
- Reverse transcriptase converts mRNA into cDNA, which lacks introns.
- The quality of the starting mRNA is the single most important factor in library quality.
- Directional cloning into an expression vector is essential for functional studies.
- Normalized and subtracted libraries are used to address the problem of transcript abundance.
- Screening methods must be matched to the nature of the target (DNA, protein, or function).
- Common pitfalls include mRNA degradation, incomplete synthesis, and chimeric clones.

## Frequently Asked Questions

### What is a cDNA library?

A cDNA library is a collection of cloned DNA fragments that are complementary to the mRNA molecules present in a particular cell or tissue at a given time. It represents the expressed genes of that sample, with each clone corresponding to a specific mRNA transcript.

### What are the steps to construct a cDNA library?

The steps are: (1) isolate mRNA from the source tissue, (2) synthesize first-strand cDNA using reverse transcriptase and an oligo(dT) or random primer, (3) synthesize second-strand cDNA using RNase H and DNA polymerase I, (4) ligate the double-stranded cDNA into a vector using linkers or adapters, and (5) transform the recombinant vectors into competent *E. coli* cells and amplify the library.

### What is the difference between a cDNA library and a genomic library?

A cDNA library is made from mRNA and contains only expressed, intron-free coding sequences. A genomic library is made from total genomic DNA and contains all sequences, including introns, regulatory regions, and repetitive DNA, regardless of whether they are expressed.

### What are the applications of a cDNA library?

cDNA libraries are used for gene cloning and discovery, studying gene expression patterns, constructing expression libraries for protein production, identifying differentially expressed genes, and isolating full-length coding sequences for functional analysis.

### Why is mRNA used to make a cDNA library?

mRNA is used because it represents the expressed genes of a cell and has already undergone splicing, removing introns. This makes the cDNA directly usable for expression in bacteria or other heterologous systems, which cannot process introns.

### What is a normalized cDNA library?

A normalized cDNA library is one in which the frequency of each clone has been equalized, so that rare transcripts are represented at a similar frequency to abundant transcripts. This is achieved by denaturing the cDNA and removing the rapidly reannealing (abundant) fraction.

### What are common problems when constructing a cDNA library?

Common problems include mRNA degradation by RNases, incomplete first-strand synthesis due to secondary structure, chimeric clones from improper ligation, and underrepresentation of rare transcripts. These issues can be mitigated by careful technique, using thermostable enzymes, size fractionation, and normalization.

## Key Takeaways

- A cDNA library is a collection of cloned DNA copies of mRNA, representing the expressed genes of a cell or tissue.
- The construction process involves mRNA isolation, reverse transcription, second-strand synthesis, vector ligation, and transformation.
- cDNA libraries lack introns and regulatory sequences, making them distinct from genomic libraries.
- Specialized libraries—normalized, subtracted, and full-length—are designed to overcome specific limitations of standard libraries.
- Screening methods include hybridization with nucleic acid probes, immunodetection with antibodies, and functional assays.
- The quality of the starting mRNA is the most critical factor; degradation leads to truncated and non-representative libraries.
- cDNA libraries remain essential for gene cloning, expression analysis, and recombinant protein production, even in the era of high-throughput sequencing.

## Further Reading

- Zhu YY et al. *Reverse transcriptase template switching: a SMART approach for full-length cDNA library construction*. BioTechniques. 2001. [PubMed 11314272](https://doi.org/10.2144/01304pf02)
- Kooiker M, Xue GP. *cDNA library preparation*. Methods in [molecular biology](/blog/careers/molecular-biology) (Clifton, N.J.). 2014. [PubMed 24243194](https://doi.org/10.1007/978-1-62703-715-0_5)
- Swaroop A. *cDNA library*. Investigative ophthalmology & visual science. 1997. [PubMed 9152223](https://pubmed.ncbi.nlm.nih.gov/9152223/)
- Niu D et al. *cDNA library construction of two human Demodexspecies*. Acta parasitologica. 2017. [PubMed 28426424](https://doi.org/10.1515/ap-2017-0043)
- Becker KG et al. *Analysis of a sequenced cDNA library from multiple sclerosis lesions*. Journal of neuroimmunology. 1997. [PubMed 9209265](https://doi.org/10.1016/s0165-5728(97)00045-3)
- Hu L et al. *The Construction of Full-Length cDNA Library for Otodectes cynotis*. Acta parasitologica. 2019. [PubMed 30864098](https://doi.org/10.2478/s11686-019-00034-y)

## Related Topics

- [Gibson Assembly](/knowledge/molecular-biology/gibson-assembly)
- [Golden Gate Cloning](/knowledge/molecular-biology/golden-gate-cloning)
- [Shuttle Vector](/knowledge/molecular-biology/shuttle-vector)


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