Phasmids

Phasmids (from the Greek. Φάγος - devouring and English. Plasmid , from the Greek. Πλάσμα - something educated, formed) - molecular vectors , which are artificial hybrids between the phage and plasmid . Phasmids after the insertion of foreign DNA can under some conditions develop as phages, and in others as plasmids.

A phasmid is a plasmid that contains the origin of replication f1 from ^[1] . It can be used to clone a vector in combination with a . A phasmid can replicate as a plasmid, and can also be packaged as single-stranded DNA into viral particles. Phasmids contain the for double-stranded replication, as well as f1 Ori for incorporating single-stranded replication and packing into phage particles ^[1] . Many commonly used plasmids contain f1 Ori and are thus phasmids. Like plasmids, they are used to clone DNA fragments using techniques such as transformation and electroporation . Nevertheless, an infection of a bacterial host containing a phasmid with an assistant phage, for example, VCSM13 or M13K07, which provides the necessary viral components so that single-stranded DNA (ssDNA) is replicated and packaged in phage particles. The helper phage infects the bacterium, first attaching to its saws , and then, after attachment, transports its genome into the cytoplasm of the host cell. Inside the cell, the phage genome initiates the production of phasmid single-stranded DNA in the cytoplasm. This phasmid DNA is then packaged in phage particles. Phage particles containing ssDNA are released from the bacterial cell into the extracellular medium. Filamentous phages inhibit the growth of bacteria, but, unlike phage λ and usually do not cause lysis . Assistant phages, as a rule, are designed in such a way that DNA packaging in them is less efficient (due to a defective replication start site) ^[2] than phasmid packaging so that the obtained phage particles contain mainly phasmid DNA. An infection of the filiform phage F1 requires pyli, so only bacterial hosts containing an F plasmid or its derivatives can be used to obtain phage particles. Prior to the development of cyclic sequencing, the phasmids were used to produce a single-stranded DNA template. Today, phasmids are still used to create templates for site-specific mutagenesis . A detailed description of the life cycle of the filamentous phage and structural features led to the development of phage display technology, in which a number of peptides and proteins can be expressed as fusion shell proteins of the phage on the surface of the viral particle. The expressed peptides and polypeptides are inserted into the corresponding coding region of DNA in the phage and therefore this method is suitable for studying protein-protein interactions and other ligand / receptor combinations.