Pseudomonas phage Φ6

Φ6 (Phi 6) is the best-studied bacteriophage of the virus family Cystoviridae. It infects Pseudomonas bacteria (typically plant-pathogenic P. syringae). It has a three-part, segmented, double-stranded RNA genome, totalling ~13.5 kb in length. Φ6 and its relatives have a lipid membrane around their nucleocapsid, a rare trait among bacteriophages. It is a lytic phage, though under certain circumstances has been observed to display a delay in lysis which may be described as a "carrier state". Proteins The genome of Φ6 codes for 12 proteins. P1 is a major capsid protein which is responsible of forming the skeleton of the polymerase complex. In the interior of the shell formed by P1 is the P2 viral replicase and transcriptase protein. The spikes binding to receptors on the Φ6 virion are formed by the protein P3. P4 is a nucleoside-triphosphatase which is required for the genome packaging and transcription. P5 is a lytic enzyme. The spike protein P3 is anchored to a fusogenic envelope protein in P6. P7 is a minor capsid protein, P8 is responsible of forming the nucleocapsid surface shell and P9 is a major envelope protein. P12 is a non-structural morphogenic protein shown to be a part of the envelope assembly. P10 and P13 are proteins coding genes that are associated with the viral envelope and P14 is a non-structural protein. Life cycle Φ6 typically attaches to the Type IV pilus of P. syringae with its attachment protein, P3. It is thought that the cell then retracts its pilus, pulling the phage toward the bacterium. Fusion of the viral envelope with the bacterial outer membrane is facilitated by the phage protein, P6. The muralytic (peptidoglycan-digesting) enzyme, P5, then digests a portion of the cell wall, and the nucleocapsid enters the cell coated with the bacterial outer membrane.