User:Jnashl24/Escherichia virus T4

What can be expanded upon: (underlined is my additions)

• Genome
• Translation
• Virus Particle Structure
• Transcription section absent

Transcription

Infection and transcription for T-even phages require the use of the host core RNA polymerase. Transcription uses 3 classes of promoters - early, middle, and late. In each of these developmental stages, multiple T4 promoters are competing with the bacterial promoters for the 2,000 RNA polymerase holoenzymes. In the early stage of transcription 39 T4 early promoters are used, 30 T4 middle promoters are used in the middle stage, and up to 50 T4 late promoters are used during the last stage. The late stage of transcription is the stage responsible for the synthesis of T4 body and fiber proteins.

Virus Particle Structure

T4 is a relatively large virus, at approximately 90 nm wide and 200 nm long (most viruses range from 25 to 200 nm in length). The DNA genome is held in an icosahedral head, also known as a capsid, and 40% of the genome is responsible for the synthesis and assembly of the virus body. The T4’s tail is hollow so that it can pass its nucleic acid into the cell it is infecting after attachment. The tail is made up of two slender cocylinders and a baseplate with the inner cylinder consisting of 144 subunits of gp19 arranged in 24 stacked hexameric rings. The outer cylinder, arranged in the same organization, consists of 144 subunits of gp18. Myoviridae phages, like T4, have complex contractile tail structures with a large number of proteins involved in the tail assembly and function. The tail fibres are also important in recognizing host cell surface receptors, so they determine if a bacterium is within the virus's host range.

The structure of the 6 megadalton T4 baseplate that comprises 127 polypeptide chains of 13 different proteins (gene products 5, 5.4, 6, 7, 8, 9, 10, 11, 12, 25, 27, 48 and 53) has recently been described in atomic detail. An atomic model of the proximal region of the tail tube formed by gp54 and the main tube protein gp19 have also been created. The tape measure protein gp29 is present in the baseplate-tail tube complexes, but it could not be modeled.