Genomic library

To build a genomic library, DNA is extracted from cells and then digested with restrictase enzyme to cut DNA into fragments of a certain size ^{[1] [2]} . Fragments are then inserted into the vector using the DNA ligase enzyme. Further, the DNA vector can be integrated into the host organism — usually into a population of Escherichia coli ( E. coli ) or yeast , where each cell contains copies of the vector with one, unique insert.

Using the host cell to store the vector makes it easy to amplify and locate specific clones from the library for analysis. The genomic library can be stored for a long time (in a frozen state). If necessary, individual bacterial or yeast clones containing DNA fragments with the desired genes or other elements of the genome are isolated and propagated ( cloned ). Cloned in this way parts of the genome are isolated from cells and used to solve various theoretical and practical problems of genetics , medicine (including the diagnosis of hereditary diseases ) and biotechnology , as well as for mapping genomes ^{[3] [4] [5]} .

Screening (from the English screening ) library, that is, the search for a specific DNA fragment among hundreds and thousands of other sequences, is carried out by DNA hybridization using DNA probes ^[3] . If the researcher knows at least a small sequence of nucleotides from the desired site, he artificially synthesizes a complementary sequence ( primer about 20 nucleotides in length) and labels it with either a radioactive isotope or a fluorescent label. A replica is made from a Petri dish with colonies by blotting : a thin nitrocellulose or other membrane is applied to the cup, on which the imprint of all colonies remains. After that, the destruction of bacterial cells on the fingerprint, the release of DNA from proteins in an alkaline medium, and DNA denaturation to a single-stranded molecule are carried out. Then, all colonies are treated with a probe and they look into which of the colonies the probe joined according to the principle of complementarity. This colony will contain the desired DNA fragment.

Sometimes the researcher does not know the DNA sequence that he is looking for, but has the amino acid sequence of the protein under investigation. Since each amino acid can correspond to several triplets of nucleotides (from one to six), the probable coding DNAs can be different. Then a mixture of probes is prepared that can recognize the intended sequence.

Modern high-tech methods for screening genomic libraries (in particular, made using vectors ) are based on the use of robotic (automated) production , in any required number of copies, microplates for storing colonies (clones), as well as nitrocellulose and nylon membranes ( filters) used directly for hybridization with DNA probes. In this case, a further increase in the screening efficiency is achieved through the use of so-called overgos samples as DNA probes (from the English over lapping oligos - “overlapping oligonucleotides ”) ^{[3] [6]} . It is also possible to use PCR for screening libraries.

Another variety of the genomic library is the microsatellite library, the clones of which contain tandem repeats . Their sequencing allows one to obtain polymorphic DNA markers (microsatellite loci ) for various genetic and genomic applications ^[7] .

• Vector (molecular biology)
• DNA cloning
• English b: Structural Biochemistry / DNA recombinant techniques / Artificial Chromosomes / Bacterial Artificial Chromosomes (BAC)
• English b: Structural Biochemistry / DNA recombinant techniques / Genomic Library

• Schelkunov S. N. Genetic engineering. - 2nd ed. - Novosibirsk : Siberian University Publishing House, 2004. - 496 p. - 2000 copies. - ISBN 5940870988 .