Biochemistry

A Frozen Giant

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Science  23 Sep 2005:
Vol. 309, Issue 5743, pp. 1967-1969
DOI: 10.1126/science.309.5743.1967e

Mimivirus (so-named because when subjected to Gram staining it, resembles or mimics a microbe) was first identified a decade ago as a virus growing within amoebae during an outbreak of pneumonia. Since then, its genome has been sequenced and, at 1.2 Mb, shown to be larger than the genomes of some bacteria and to contain more than 1000 open reading frames (potential protein-encoding genes).

Using cryoelectron microscopy, Xiao et al. report that the outer protein shell of the virus is about 5000 Å in diameter and supports a dense mesh of 1250 Å-long fibers that may be collagen triple helices. Inside the capsid are two lipid membranes that surround the supersized genome. A three-dimensional reconstruction to 75 Å resolution is consistent with icosahedral symmetry and an impressively high triangulation number of 1179, indicative of a remarkably accurate assembly of protein subunits into the capsid. — GJC

J. Mol. Biol. 10.1016/j.jmb.2005.08.060 (2005).

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