F1 phage
| F1 phage | |
|---|---|
| Virus classification | |
| Group: | Group II (ssDNA) |
| Family: | Inoviridae |
| Genus: | Inovirus |
| Species | |
|
Enterobacteria phage f1 |
|
Enterobacteria phage f1
Bacteriophage f1 is structurally classified as a class I filamentous phage, and is closely related to the other Ff phages, such as M13 and phage fd.
In the following article, genes will be written in italics and their associated proteins in Roman.
Phage f1 is a filamentous (rod-shaped) ssDNA phage, with a molecular mass of about 1.6×107 Da; by weight it is 11.3 percent DNA. The flexible phages are about 850 nm long and 4.3 or 6.3 nm wide. The thousands of identical major coat proteins that make up the sheath are arranged in a fishcale-like α-helix.
The ends of the filament are sealed with protein caps; the blunt end contains 3–5 copies of each VII and IX, while the terminally extruded bead-like end contains about 5 copies each of III and VI.
f1 has a circular, 6407 bp genome of ss-DNA.
There are 11 genes encoded on the genome; two are overlapping in-frame genes. Five of the encoded proteins make up the , three are needed for synthesis and the rest are for assembly. The genes are generally referred to by Roman numerals I-XI, and are in the order II(X), V, VII, IX, VIII, III, VI, I(XI), IV, intergenic region (IG or IGR). The IGR contains the packing signal (PS) as well as sequences that dictate termination, nicking for replication, and the binding of II and IHF.
f1 is male specific; it only infects Hfr or F+ strains of E. coli.
Several host proteins are required for infection and depolymerization of the coat proteins of the phage. A domain of III binds to the primary receptor, the tip of the F pilus, and retraction of the pilus by an unknown mechanism brings another domain of III close enough to the membrane to bind the coreceptor, host tolA.
The removal of the cap proteins and release of the ssDNA into the cytoplasm are both mediated by the interactions of tolA and III. A hydrophobic portion of III inserts itself into the inner membrane, fastening the phage particle to the host and distributing the coat proteins into the host membrane. It is the degradation of the major coat protein that causes the genome to be released into the cytoplasm of the host.
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Wikipedia