Leave It to Mimi

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Science  16 May 2008:
Vol. 320, Issue 5878, pp. 850
DOI: 10.1126/science.320.5878.850b

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Acanthamoeba polyphaga mimivirus is a very large double-stranded DNA virus (genome size of 1.2 megabase pairs). By examining images of infected amoebae with electron tomography and cryo-scanning electron microscopy, Zauberman et al. have deduced how the genome is released from and packaged into the icosahedral viral capsid. Other DNA viruses have been observed to use a single icosahedral vertex both for loading DNA during viral biogenesis and for releasing it upon entering the host cell. In contrast, mimivirus appears to use two distinct portals. When feeding its genome into newly assembled viral capsids, a passageway at the center of an icosahedral face is used; when releasing its DNA, the mimivirus capsid undergoes a large conformational opening of five icosahedral faces around a single vertex. This so-called stargate serves as a membrane-lined sleeve through which the whole viral genome can escape promptly after infection. These entry and exit strategies may also be used by other large DNA-containing viruses, especially those that, like mimivirus, contain an internal membrane and encode proteins related to the DNA-packaging ATPases that are involved in bacterial DNA segregation, another process during which a large amount of DNA passes through a membrane portal. — SMH

PLOS Biol. 6, e114 (2008).

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