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How a parasite changes its molecular coat


The deadly trypanasome parasite, which infects thousands of Africans with sleeping sickness each year, evades the human immune system by repeatedly changing its molecular coat. A new study describes how this happens. The key is an unusual transcription factory in the cell that switches genes on and off to produce the diverse coats that cover the parasite.

Miguel Navarro and Keith Gull, of the University of Manchester's School of Biological Sciences in Manchester, U.K., found that those factories produce one of a family of variant surface glycoprotein (VSG) genes at any given time. By making such rapid coat changes, the Trypanosoma brucei parasite confuses the human immune system, which is unable to mount an effective response to kill the parasite.

The researchers used green fluorescent protein tags to show that the VSG expression sites are produced outside of the ribosome-producing nucleolus. They call the newly-defined structure the Expression Site Body (ESB).

"The ESB that we have identified represents direct evidence for the existence of a highly defined individual transcription factory," the researchers write in Nature. Their model, which links such ESB factories to particular genes, could help to explain similar expression characteristics in malaria and other parasites.

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Navarro, M. & Gull, K. A pol I transcriptional body associated with VSG mono-allelic expression in Trypanosoma brucei. Nature 414, 759-763 (December 13, 2001).

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