Phagemid

Source: Wikipedia, the free encyclopedia.

A phagemid or phasmid is a DNA-based cloning vector, which has both bacteriophage and plasmid properties.[1] These vectors carry, in addition to the origin of plasmid replication, an origin of replication derived from bacteriophage. Unlike commonly used plasmids, phagemid vectors differ by having the ability to be packaged into the capsid of a bacteriophage, due to their having a genetic sequence that signals for packaging. Phagemids are used in a variety of biotechnology applications; for example, they can be used in a molecular biology technique called "phage display".[2]

The term "phagemid" or "phagemids" was coined by a group of Soviet scientists, who discovered them, named them, and published the article in April 1984 in Gene magazine.[3]

Properties of the cloning vector

A phagemid (plasmid + phage) is a

origin of replication (ori) for double stranded replication, as well as an f1 ori to enable single stranded replication and packaging into phage particles.[4]
Many commonly used plasmids contain an f1 ori and are thus phagemids.

Similarly to a plasmid, a phagemid can be used to clone DNA fragments and be introduced into a bacterial host by a range of techniques, such as

transformation and electroporation
. However, infection of a bacterial host containing a phagemid with a 'helper' phage, for example VCSM13 or M13K07, provides the necessary viral components to enable single stranded DNA replication and packaging of the phagemid DNA into phage particles. The 'helper' phage infects the bacterial host by first attaching to the host cell's pilus and then, after attachment, transporting the phage genome into the cytoplasm of the host cell. Inside the cell, the phage genome triggers production of single stranded phagemid DNA in the cytoplasm. This phagemid DNA is then packaged into phage particles. The phage particles containing ssDNA are released from the bacterial host cell into the extracellular environment.

Filamentous phages retard bacterial growth but, contrasting with the lambda phage and the T7 phage, are not generally lytic. Helper phages are usually engineered to package less efficiently (via a defective phage origin of replication)[5] than the phagemid so that the resultant phage particles contain predominantly phagemid DNA. F1 Filamentous phage infection requires the presence of a pilus so only bacterial hosts containing the F-plasmid or its derivatives can be used to generate phage particles.

Prior to the development of cycle sequencing, phagemids were used to generate single stranded DNA template for sequencing purposes. Today phagemids are still useful for generating templates for

protein-protein interactions
and other ligand/receptor combinations.

References

  1. ^ Wilson, K.; Walker, J. (2010). Principles and Techniques of Biochemistry and Molecular Biology. 7th ed. New York: Cambridge University Press. p. 751.
  2. ISBN 978-087969740-2
    .
  3. PMID 6234200
    .
  4. ^
    ISBN 978-0-470-09157-9
    .
  5. PMID 19998056
    .
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