Enterobacteria phage T4
The T4 phage ( bacteriophage T4 earlier, T4 bacteriophage ) infection of a bacteriophage of Escherichia coli bacteria. He is with its morphology as a " prototype " of bacteriophages and had in virological research an important significance for understanding the reproductive strategy of phages and viruses, and general genetics (see also Hershey - Chase experiment, Max Delbrück ).
Structure
As a member of the order Caudovirales, Myoviridae genus is the genome of the phage T4 from a single, double-stranded DNA molecule that is completely sequenced with its length of 168 903 bp. It covers about 300 genes and renders 48 % of the weight of the virion from. DNA contains, in addition to the normal nucleotide in place of cytosine, 5- hydroxymethylcytosine, which may additionally be glycosylated by a glucose residue. This glycosylation of the DNA is believed to be responsible for the control of gene expression. The reading direction of the circular genome are alternately reversed and at the end there are redundant portions. Within the capsid, the DNA is arranged periodically according to a complex packing scheme.
The capsid of the T4 phage is basically icosahedral, however, is a different from the basic form, elongated stretch especially typical for this species ( " elongated pentagonal bipyramidal antiprismatic "). It consists of 152 capsomeres and is about 111 nm long and 78 nm in size in diameter. The contractile tail is 113x16 nm in size and consists of a piece neck (collar ), a base plate, attach to the six short spikes and six long tail fibers. In the replication of T4 phage caused a number of structurally unstable or DNA packaged malformations ( Mehrfachkapside, not stretched icosahedron ) of the capsid, which is not surprising due to the highly complex structure. The virion consists of a total of 49 different proteins.
It can be distinguished by different properties of the antigen binding eight serological subsets of T4 phage. Taxonomic subtypes of T4 phage species are: Enterobacteria phage C16, F10, Fsα, PST, SKII, SKV, SKX, SV3, T2, T4 and T6. The T2 phage (formerly a separate species) is thus only a subtype of the T4 phage.
Infection cycle
The infection cycle takes about 30 min. For this purpose the phage docked to the ends of the tail fibers in Porinproteine to the outer membrane of E. coli. The tail sting with Lysozymfunktion breaks the cell wall enzymatically and the phage DNA is injected through the tail into the interior of the cell. Here, the DNA is first transcribed and translated by the bacterial enzymes. The newly - formed phage polymerase then replicates the phage genes. Even during which begins the synthesis of the phage coat. In this, the replicated DNA is finally packaged. Last phage - specific lysozyme is synthesized, which destroys the cell walls of the bacteria. Thus the finished phages are released.
Special
The T4 phage have an extremely rapid DNA synthesis apparatus, thanks to the viral DNA polymerase type B with an error rate of only one exchange to 300 genome copies. It has special DNA repair mechanisms, which otherwise occur only in eukaryotic cells.
In molecular biology and genetic engineering the DNA ligase of the phage T4 is of great importance, it is also briefly referred to as T4 ligase.