A phagemid or phasmid is a type of cloning

Cloning

Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...

 vector

Vector (molecular biology)

In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, viruses, cosmids, and artificial chromosomes...

 developed as a hybrid of the filamentous phage

Filamentous phage

A filamentous phage is a type of bacteriophage shaped like a rod filament. Filamentous phages usually contain a genome of single-stranded DNA and infect Gram-negative bacteria.-Types of filamentous phage:*Ff phages - these infect E...

 M13

M13 phage

M13 is a filamentous bacteriophage composed of circular single stranded DNA which is 6407 nucleotides long encapsulated in approximately 2700 copies of the major coat protein P8, and capped with 5 copies of two different minor coat proteins on the ends. The minor coat protein P3 attaches to the...

 and plasmid

Plasmid

In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...

s to produce a vector that can grow as a plasmid, and also be packaged as single stranded DNA in viral particles. Phagemids contain an origin of replication (ori)

Ori (genetics)

Ori is the DNA sequence that signals for the origin of replication, sometimes referred to simply as origin. In E. coli, ori is some 250 nucleotides in length for the chromosomal origin...

 for double stranded replication, as well as an f1 ori to enable single stranded replication and packaging into phage particles. 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 (transformation, 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. These are secreted through the cell wall and released into the medium. Filamentous phage retard bacterial growth but, in contrast to lambda and T7 phage

T7 phage

Bacteriophage T7 is a bacteriophage capable of infecting susceptible bacterial cells. It infects most strains of Escherichia coli Bacteriophage T7 is a bacteriophage capable of infecting susceptible bacterial cells. It infects most strains of Escherichia coli Bacteriophage T7 is a bacteriophage...

, are not generally lytic. Helper phage are usually engineered to package less efficiently than the phagemid so that the resultant phage particles contain predominantly phagemid DNA. F1 Filamentous phage infection requires the presence of a pilus

Pilus

right|thumb|350px|Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, brings the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is then transferred to the recipient cell...

 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 site-directed mutagenesis

Site-directed mutagenesis

Site-directed mutagenesis, also called site-specific mutagenesis or oligonucleotide-directed mutagenesis, is a molecular biology technique in which a mutation is created at a defined site in a DNA molecule. In general, this form of mutagenesis requires that the wild type gene sequence be known...

. Detailed characterisation of the filamentous phage life cycle and structural features lead to the development of phage display

Phage display

Phage display is a method for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages to connect proteins with the genetic information that encodes them. Phage Display was originally invented by George P...

 technology, in which a range of peptides and proteins can be expressed as fusions to phage coat proteins and displayed on the viral surface. The displayed peptides and polypeptides are associated with the corresponding coding DNA within the phage particle and so this technique lends itself to the study of protein-protein interaction

Protein-protein interaction

Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

s and other ligand/receptor combinations.