A P1-derived artificial chromosome, or PAC, is a

DNA construct A DNA construct is an artificially-designed segment of DNA borne on a vector that can be used to incorporate genetic material into a target tissue or cell. A DNA construct contains a DNA insert, called a transgene, delivered via a transformation ...

derived from the DNA of P1 bacteriophages and

Bacterial artificial chromosome A bacterial artificial chromosome (BAC) is a DNA construct, based on a functional fertility plasmid (or F-plasmid), used for transforming and cloning in bacteria, usually '' E. coli''. F-plasmids play a crucial role because they contain partiti ...

. It can carry large amounts (about 100–300 kilobases) of other sequences for a variety of bioengineering purposes in

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. It is one type of the efficient cloning

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

used to clone DNA fragments (100- to 300-kb insert size; average,150 kb) in ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' cells.

History of PAC

The bacteriophage P1 was first isolated by Dr. Giuseppe Bertani. In his study, he noticed that the lysogen produced abnormal non-continuous phages, and later found phage P1 was produced from the Lisbonne lysogen strain, in addition to bacteriophages P2 and P3. P1 has the ability to copy a bacteria's host genome and integrate that DNA information into other bacteria hosts, also known as generalized transduction. Later on, P1 was developed as a cloning vector by

Nat Sternberg Nat L. Sternberg (August 2, 1942 – September 26, 1995) was an American molecular biologist and bacteriophage researcher, particularly known for his work on DNA recombination and the phage P1. Early life and education Born in 1942 in Brooklyn ...

and colleagues in the 1990s. It is capable of

Cre-Lox recombination Cre-Lox recombination is a site-specific recombinase technology, used to carry out deletions, insertions, translocations and inversions at specific sites in the DNA of cells. It allows the DNA modification to be targeted to a specific cell type ...

. The P1 vector system was first developed to carry relatively large DNA fragments in plasmids (95-100kb).

Construction

PAC has 2 ''loxP'' sites, which can be used by phage recombinases to form the product from its ''cre-''gene recognition during

. This process circularizes the DNA strand, forming a plasmid, which can then be inserted into bacteria such as

. The transformation is usually done by

electroporation Electroporation, or electropermeabilization, is a microbiology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, electrode arrays or DNA to be introd ...

, which uses electricity to allow the plasmids permeate into the cells. If high expression levels are desired, the P1 lytic replicon can be used in constructs.

Electroporation Electroporation, or electropermeabilization, is a microbiology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, electrode arrays or DNA to be introd ...

allows for lysogeny of PACs so that they can replicate within cells without disturbing other chromosomes.

Comparison with Other Artificial Chromosomes

PAC is one of the artificial chromosome vectors. Some other artificial chromosomes include:

bacterial artificial chromosome A bacterial artificial chromosome (BAC) is a DNA construct, based on a functional fertility plasmid (or F-plasmid), used for transforming and cloning in bacteria, usually '' E. coli''. F-plasmids play a crucial role because they contain partiti ...

yeast artificial chromosome Yeast artificial chromosomes (YACs) are genetically engineered chromosomes derived from the DNA of the yeast, ''Saccharomyces cerevisiae'', which is then ligated into a bacterial plasmid. By inserting large fragments of DNA, from 100–1000 ...

and the

human artificial chromosome A human artificial chromosome (HAC) is a microchromosome that can act as a new chromosome in a population of human cells. That is, instead of 46 chromosomes, the cell could have 47 with the 47th being very small, roughly 6–10 megabases (Mb) in si ...

. Compared to other artificial chromosomes, it can carry relatively large DNA fragments, however less so than the

(YAC). Some advantages of PACs compared to YACs includes easier manipulation of bacteria system, easier separation from DNA hosts, higher transformation rate, more stable inserts, and they are non-chimeric which means they do not rearrange and ligate to form new DNA strand, allowing for a user friendly vector choice.

Applications

PAC is commonly used as a large capacity vector which allows propagation of large DNA inserts in

. This feature has been commonly used for: * building genome libraries for human, mouse, etc, helps with projects such as Human Genome Project * libraries served as the template for gene sequencing (example: used as gene template in mouse gene function analysis) * genome analysis on specific functions of different genes for more complex organisms (plants, animals etc.) * facilitate gene expression Since PAC was derived from phages, PAC and its variants are also useful in the PAC-based phage therapy and antibiotic studies.

References

External links