Phage f1: Difference between revisions
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Phage f1 is a filamentous (rod-shaped) ssDNA phage, with a molecular mass of about 1.6x10<sup>7</sup> Da; by weight it is 11.3 percent DNA. <ref name='PMID:7616570'/> <ref name='PMID:14065763'/> The flexible rods are about 8500 Å (850 nm) long, and depending on the staining technique, appear to be 43 or 63 Å wide. <ref name='PMID:14065763'/> The thousands of identical major coat proteins that make up the sheath are slightly curved, enlongated proteins about 70 Å by 10 Å arranged in an α-helix. <ref name='PMID:21082179'/> <ref name='PMID:9631287'/> These sheath proteins slightly overlap and are oriented just slightly off of perpendicular (20°) to the length of the filament; they are interdigitated and slope radially (with a 5-fold rotation axis and 2-fold helical axis) to form a fishscale-like envelope for the DNA core. <ref name='PMID:21082179'/> <ref name='LIB:Bacteriophages'/> | Phage f1 is a filamentous (rod-shaped) ssDNA phage, with a molecular mass of about 1.6x10<sup>7</sup> Da; by weight it is 11.3 percent DNA. <ref name='PMID:7616570'/> <ref name='PMID:14065763'/> The flexible rods are about 8500 Å (850 nm) long, and depending on the staining technique, appear to be 43 or 63 Å wide. <ref name='PMID:14065763'/> The thousands of identical major coat proteins that make up the sheath are slightly curved, enlongated proteins about 70 Å by 10 Å arranged in an α-helix. <ref name='PMID:21082179'/> <ref name='PMID:9631287'/> These sheath proteins slightly overlap and are oriented just slightly off of perpendicular (20°) to the length of the filament; they are interdigitated and slope radially (with a 5-fold rotation axis and 2-fold helical axis) to form a fishscale-like envelope for the DNA core. <ref name='PMID:21082179'/> <ref name='LIB:Bacteriophages'/> | ||
The ends of the filament are sealed with | The ends of the filament are sealed with protein caps. The end that is extruded first appears blunt and contains several copies of each pVII and pIX, while 3-5 copies of pIII and pVI seal off the terminally extruded end and give it a bead-like appearance.<ref name='LIB:Bacteriophages'/> <ref name='PMID:10404600'/> | ||
== Genome Organization == | == Genome Organization == | ||
Revision as of 18:51, 28 June 2011
Bacteriophage f1 is structurally classified as a class I filamentous phage, and is closely related to the other Ff phages, Phage M13 and phage fd. [1] [2]
The full sequence is available from NCBI at GenBank: J02448.1
Phage f1, a ssRNA phage, should not be confused with phage F1, a ssDNA phage, but f1 may also refer to a ssDNA phage.
Morphology
Phage f1 is a filamentous (rod-shaped) ssDNA phage, with a molecular mass of about 1.6x107 Da; by weight it is 11.3 percent DNA. [3] [4] The flexible rods are about 8500 Å (850 nm) long, and depending on the staining technique, appear to be 43 or 63 Å wide. [4] The thousands of identical major coat proteins that make up the sheath are slightly curved, enlongated proteins about 70 Å by 10 Å arranged in an α-helix. [5] [6] These sheath proteins slightly overlap and are oriented just slightly off of perpendicular (20°) to the length of the filament; they are interdigitated and slope radially (with a 5-fold rotation axis and 2-fold helical axis) to form a fishscale-like envelope for the DNA core. [5] [1]
The ends of the filament are sealed with protein caps. The end that is extruded first appears blunt and contains several copies of each pVII and pIX, while 3-5 copies of pIII and pVI seal off the terminally extruded end and give it a bead-like appearance.[1] [2]
Genome Organization
f1 has a circular, 6407 bp genome of ss-DNA.
There are 10 genes encoded on the genome; they are generally referred to by Roman numerals I-X as listed on the f1 Gene page. Genes are in the order II (X), V, VII, IX, VIII, III, VI, I, IV, intergenic region (IG or IGR). [1]
Life cycle
Adsorption and Injection
f1 is male specific; it only infects Hfr or F+ strains of E. coli. [4] The pIII N2 domain binds to the primary receptor, the tip of the F pilus, and retraction of the pilus allows another domain of pIII (N1) to bind to the coreceptor tolA.[2] This host protein, along with tolQ and tolR, are required for infection and degrade the coat proteins of the phage, distributing them into the membrane. [2][1] The removal of the cap proteins releases the ssDNA into the cytoplasm.
DNA replication
The ssDNA genome is replicated and translated with host enzymes. For replication, the dsDNA remains in a supercoiled RF and uses rolling circle replication once the complement strand has been synthesized.
Packaging
Accumulation of pV allows the formation of a DNA-pV complex, hundreds of which can form per host. [2] The complexes prevent further copies of the complement strand from being made, and also "pre-package" the DNA into an almost linear form. [2] About 1500 copies of pV as dimers form a flexible, semi-enclosed left-handed helix about 8x800-900 nm that encapsulate the DNA. [2][1] The ssDNA does not interact with itself inside the capsule, and remains untwisted and unpaired.
A packaging signal, PS, exists in the IGR as an imperfect hairpin and is responsible for anchoring and the proper orientation of the genome in the phage. [1] It remains partially exposed at one end of the complex
The phage envelope consists of about 2700 copies of the major coat protein encoded by pVIII. [7] As with most filamentous phages, there is no defined limit on the amount of DNA that can be packaged into the phage coat (contrast to phages with set capsid size, such as phage λ) although larger inserts are naturally selected against. [1]
The proteins depolymerized upon phage entry can be reused for the packaging of new phage, and as with newly synthesized coat proteins pIII pVI pVII pVIII and pIX, remain as integral membrane proteins until needed. [1]
Lysis
This phage does not lyse its host, but can extrude many copies of itself throughout the life of the host cell. Excessive copies of the phage genome can be packaged, called "polyphage", but these are due to improper termination of extrusion. [1]
See also
References
See Help:References for how to manage references in EcoliWiki.
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Edited by Richard Calendar (2006) The Bacteriophages (Oxford University Press, Oxford, NY) ISBN 0-19-514850-9
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Lubkowski, J et al. (1999) Filamentous phage infection: crystal structure of g3p in complex with its coreceptor, the C-terminal domain of TolA. Structure 7 711-22 PubMed
- ↑ Endemann, H & Model, P (1995) Location of filamentous phage minor coat proteins in phage and in infected cells. J. Mol. Biol. 250 496-506 PubMed
- ↑ 4.0 4.1 4.2 ZINDER, ND et al. (1963) F1, A ROD-SHAPED MALE-SPECIFIC BACTERIOPHAGE THAT CONTAINS DNA. Virology 20 638-40 PubMed
- ↑ 5.0 5.1 Straus, SK et al. (2011) Consensus structure of Pf1 filamentous bacteriophage from X-ray fibre diffraction and solid-state NMR. Eur. Biophys. J. 40 221-34 PubMed
- ↑ Marvin, DA (1998) Filamentous phage structure, infection and assembly. Curr. Opin. Struct. Biol. 8 150-8 PubMed
- ↑ Haigh, NG & Webster, RE (1998) The major coat protein of filamentous bacteriophage f1 specifically pairs in the bacterial cytoplasmic membrane. J. Mol. Biol. 279 19-29 PubMed