Findings uncover new details about myster...( WEST LAFAYETTE Ind. - An internation...)

WEST LAFAYETTE, Ind. - An international team of researchers has determined key structural features of the largest known virus, findings that could help scientists studying how the simplest life evolved and whether the unusual virus causes any human diseases.

The mimivirus has been called a possible "missing link" between viruses and living cells. It was discovered accidentally by French scientists in 1992 but wasn't confirmed to be a virus until 2003.

The virus infects amoebas, but it is thought to possibly be a human pathogen because antibodies to the virus have been discovered in pneumonia patients. However, many details about the virus remain unknown, said Michael Rossmann, Purdue University's Hanley Distinguished Professor of Biological Sciences.

Now a team of researchers from Purdue, the University of California at Irvine and the University of the Mediterranean in Marseilles, France, have thrown more light on the mimivirus' makeup.

The scientists have determined the basic design of the virus' outer shell, or capsid, and also of the hundreds of smaller units called capsomeres making up this outer shell. Findings also confirmed the existence of a starfish-shaped structure that covers a "special vertex," an opening in the capsid where genetic material leaves the virus to infect its host, and an indentation in the virus's genetic material itself is positioned opposite this opening, Rossmann said.

"The findings are important in terms of studying the evolution of cells, bacteria and viruses," said Siyang Sun, a postdoctoral research associate working in Rossmann's lab. "The mimivirus is like an intermediate between a cell and a virus. We usually think of cells as being alive and a virus is thought of as being dead because it needs a host cell to complete its life cycle. The mimivirus straddles a middle ground between viruses and living cells, perhaps redefining what a virus is."

The virus approaches the size
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