Caudovirales
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The Caudovirales are an order of viruses, better known as the tailed bacteriophages. Under the Baltimore classification scheme, the Caudovirales are group 1 viruses as they have double stranded DNA (dsDNA) genomes, which can be anywhere from 18 kbp to 500 kbp in length. The virus particles have a distinct shape; each virion has an Icosohedral head that contains the genome, which is attached to a tail by a connector. The order encompasses a wide range of viruses, many of which have the same or similar genes; however the nucleotide sequence can vary quite significantly, even amongst the same genus. Due to their characteristic structure, it is believed they share a common origin.
[edit] Infection
Upon encountering a host bacterium, the tail section of the virion binds to receptors on the cell surface, and delivers the DNA into the cell by use of an injectisome like mechanism (an injectisome is a nanomachine that evolved for the delivery of proteins, by type III secretion). The tail section of the virus punches a hole through the bacterial cell wall and plasma membrane, and the genome passes down the tail into the cell. Once inside the genes are expressed from transcripts made by the host machinery, using host ribosomes. Typically, the genome is replicated by use of concatamers, in which over lapping segments of DNA are made, and then put together to form the whole genome.
[edit] Assembly and Maturation
Viral capsid proteins come together to form a precursor prohead, into which the genome enters. Once this has occurred, the prohead undergoes maturation by cleavage of capsid subunits to form an icosohedral phage head with 5 fold symmetry. After the head maturation, the tail is joined in one of two ways: either the tail is constructed separately, and joined with the connector, or the tail is constructed directly onto the phage head. The tails consist of helix based proteins with 6 fold symmetry. After maturation of virus particles, the cell is lysed by either lysins or holins or a combination of the two.
[edit] References
Maniloffi, J., and Ackermann, H.W., 1998, “Taxonomy of bacterial viruses: establishment of tailed virus genera and the order Caudovirales”, Achievements in Virology, 143, 10
Xu, J., et al, 2004, “Conserved Translational Frameshift in dsDNA Bacteriophage Tail Assembly Genes”, Molecular Cell, 16, 1
Casjens, S.R., 2005, “Comparative genomics and evolution of the tailed-bacteriophages”, Current Opinion in Microbiology, 8, 4, 451-458
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