Genomic Library: Definition and Steps in the Construction of Genomic Library

In the last post, we discussed about the steps in recombinant DNA technology or gene cloning. In that post, we mentioned genomic library as one of the source for getting our desired gene for cloning.

Genomic Library: Definition

Genomic library represents an entire genome of an individual animal, bacteria, plant or virus under study.

or

It is the collection of cloned segments of DNA containing at least one copy of every gene from a particular organism.

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Construction of Genomic Library of a Phage

The procedure is same for all other organism.

Step 1: DNA isolation

Isolate complete DNA from the phage (or any cell under study)

Step2: Cutting isolated DNA with restriction fragments of suitable size

Restriction enzymes like Eco R1 are used to cut genome into fragments of suitable size.

Step 3: In cooperation of this fragments into a suitable vector

These fragments are cloned into a suitable vector like plasmid, cosmid etc leading to the formation of rDNA molecule.

Step 4: Introduction to a suitable host like bacterium.

Multiplication, screening, identification and characterization of clones

Introduce this rDNA molecule with DNA fragments into a host, most often E.coli bacterium. Plasmid will multiply inside forming numerous copies. We need to identify the host cells with these fragments from the rest of cells without rDNA molecule.

Step 5: Maintenance of set of clones

The host cell multiplies and forms colonies. Each colony contains cells with a DNA fragment of the phage. Maintenance of such clones or colonies containing all fragments of the phage represents genomic library of the phage.