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Concept
Phage phiX174
Résumé
The phi X 174 (or ΦX174) bacteriophage is a single-stranded DNA (ssDNA) virus that infects Escherichia coli, and the first DNA-based genome to be sequenced. This work was completed by Fred Sanger and his team in 1977. In 1962, Walter Fiers and Robert Sinsheimer had already demonstrated the physical, covalently closed circularity of ΦX174 DNA. Nobel prize winner Arthur Kornberg used ΦX174 as a model to first prove that DNA synthesized in a test tube by purified enzymes could produce all the features of a natural virus, ushering in the age of synthetic biology. In 1972–1974, Jerard Hurwitz, Sue Wickner, and Reed Wickner with collaborators identified the genes required to produce the enzymes to catalyze conversion of the single stranded form of the virus to the double stranded replicative form. In 2003, it was reported by Craig Venter's group that the genome of ΦX174 was the first to be completely assembled in vitro from synthesized oligonucleotides. The ΦX174 virus particle has also been successfully assembled in vitro. In 2012, it was shown how its highly overlapping genome can be fully decompressed and still remain functional.
This bacteriophage has a [+] sense circular single-stranded DNA genome of 5,386 nucleotides. The genome GC-content is 44% and 95% of nucleotides belong to coding genes. Because of the balance base pattern of the genome, it is used as the control DNA for Illumina sequencers.
ΦX174 encodes 11 genes, named as consecutive letters of the alphabet in the order they were discovered, with the exception of A* which is an alternative start codon within the large A genes. Only genes A* and K are thought to be non-essential, although there is some doubt about A* because its start codon could be changed to ATT but not any other sequence. It is now known that the ATT is still likely capable of producing protein within E. coli and therefore this gene may in fact be essential.
The first half of the ΦX174 genome features high levels of gene overlap with eight out of 11 genes overlapping by at least one nucleotide.
Source officielle
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