P22 phage
| Enterobacteria phage P22 | |
|---|---|
| Virus classification | |
| Group: | Group I (dsDNA) |
| Order: | Caudovirales |
| Family: | Podoviridae |
| Genus: | P22-like viruses |
| Species: | Enterobacteria phage P22 |
| P22 tail accessory factor | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | P22_Tail-4 | ||||||||
| Pfam | PF11650 | ||||||||
| InterPro | IPR020362 | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
The Enterobacteria phage P22 is a bacteriophage that infects Salmonella typhimurium. Like many phage viruses, it has been used in molecular biology to induce mutations in cultured bacteria and to introduce foreign genetic material. Upon its discovery, P22 has been used in generalized transduction and is an important tool for Salmonella genetics.
P22 shares many similarities in genetic structure and regulation with bacteriophage λ. It is a temperate double stranded DNA phage as well as a lambdoid phage since it carries control of gene expression regions and early operons similar to those of bacteriophage λ. However, the genes which encode proteins that build the virion are different from those of bacteriophage λ. P22 has a 60 nm diameter icosahedral (T=7) virion head and a short tail. This virion morphology puts P22 in the formal Podoviridae group. Traditionally, P22 is associated with viruses with similar genomic transcription patterns and life cycles including bacteriophage λ and all the other lambdoid phages. However, this relatedness seems to be overestimated. Other relatives with similar short-tailed morphology and DNA homology in the protein genes of the virion include bacteriophages λ and Ε34. Many Podoviridae, for example phages T7 and Φ29, share few DNA similarities with P22, even though their virion morphologies are similar.
P22 has a linear, double-stranded DNA chromosome within its virion that is about 44 kilobases long with blunt ends and a circular genetic map. However, its "wild type" nucleotide sequence is about 42 kilobases long. The genome of P22 has been sequenced and sixty five genes have been annotated. The sequencing results support the hypothesis that phage P22 is a virus that has evolved through extensive recombination with other viruses.
P22 research has focused on its differences from bacteriophage λ including the mechanisms by which it circularizes DNA upon infection and packages DNA into the virion. Prior to leaving the host cell, virion chromosomes are packaged into capsids from concatemers of the sequence that result from rolling circle DNA replication. The P22 packaged DNA carries a direct duplication of about 4% at both ends since the inside of the virion has more space than is filled by 100% of the sequence. This process is called "headful packaging" since replicated DNA is "stuffed" into the virion until it is full, rather than filling each virion with a single copy of the sequence. This usually encompasses 48Kb, so part of the host DNA is transferred along with the phage.
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