How is a Genomic Library Produced

A genomic library is one of the two types of DNA libraries that contain total chromosomal DNA of a particular organism. Within the genomic library, different inserts of DNA are stored in a population of identical vectors. In order to prepare a genomic library of a particular organism, genomic DNA should be isolated from the organism. Restriction enzymes digest genomic DNA at particular DNA sequences, resulting in fragments of genomic DNA. Each fragment may contain one or two genes. These fragments are inserted into a particular type of vector and are transformed into a host bacterium to prepare a DNA clone. 

Key Areas Covered

1. What is a Genomic Library
     – Definition, Facts
2. How is a Genomic Library Produced
     – Procedure, Titer, Screening

Key Terms: Genomic Library, Titer, Restriction Digestion, Screening

How is a Genomic Library Produced - Infograph

What is a Genomic Library

A genomic library is a set of DNA clones representing the entire content of DNA of a particular organism. DNA clones are propagated by replication in microorganisms. A genomic library allows researchers to isolate a DNA fragment of interest from the library for study. Genomic libraries are important in whole genome sequencing.

How is a Genomic Library Produced

The steps involved in the preparation of a genomic library are described below.

  1. Genomic DNA Extraction and purification
  2. Digestion of genomic DNA with a particular restriction enzyme – This may result in a set of DNA fragments with similar size. Each fragment may contain one or two genes of the genome.
  3. DNA fragments are inserted into a particular type of vectors – The vector is digested with the same restriction enzyme followed by ligation of inserts into the vectors. The selection of a vector depends on the size of the genome. The vector capacities are shown below.

Table 1: Vector Capacity

Type of Vector

Insert Size

Plasmids

10 kb

Bacteriophage lambda

20 kb

Cosmids

45 kb

Bacteriophage P1

70-100 kb

P1 artificial chromosome(PAC)

130-150 kb

Bacterial artificial chromosome (BAC)

120-300 kb

Yeast artificial chromosome (YAC)

250-2000 kb

4. Transformation into a host – The host is bacteria or yeast in most of the cases. A clone of a particular DNA fragment is formed during the replication of the host.

How is a Genomic Library Produced

Figure 1: Genomic Library Preparation

Determination of the Titer of the Library

The titer of the library allows researchers to understand how many transformed host cells are in the sample. It is done by diluting the transformed cells and counting the number of cells per volume.

Screening Library

Screening allows the isolation of a particular DNA fragment from the library. It can be mainly done in two ways, either by direct selection of recombinants or detection of expression. The direct selection can be done by PCR and colony hybridization.

Conclusion

A genomic library is a collection of DNA fragments that represent the entire DNA content in the genome of a particular organism. It is produced by inserting the fragmented DNA of the genome into a vector and transforming the recombinant molecules into a host cell for multiplication.

Reference:

1. Kumar, Chinnu S. “Genomic Library.” LinkedIn SlideShare, 4 Oct. 2015, Available here.

Image Courtesy:

1. “Genomic Library Construction” By Aluquette – Own work (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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