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Published: 2009-11-12

New type of gene regulation in Listeria discovered by Umeå scientists

NEWS A team of molecular biologists at Umeå University has discovered a new way of controlling gene functions used by Listeria bacteria. The findings are now published in the international journal Cell.

Text: Eva-Maria Diehl

Jörgen Johansson's research group at the Department of Molecular Biology in Umeå studies how Listeria monocytogenes control their gene functions. These bacteria cause several types of infections in humans, preferably immuno-compromised people but also pregnant women, and spread via food products, mainly in dairy products. From infected food the Listeria bacteria are able to pass the intestinal barrier and reach the blood circulation and the lymphatic system. Without medical treatment the bacteria can proliferate in the liver and spleen before infecting the brain and placenta, which often is lethal for the patient.

Genetic information encoded in DNA is the basis for the cellular synthesis of molecules, proteins, controlling cellular functions and growth. However, the ribonucleic acids (RNA) are the information officers of the cell and ensure that information is transferred from DNA to proteins. Scientists know by now that RNA plays an important role in gene regulation. Pathogenic organisms use RNA regulation to produce toxic substances during infectious processes. RNA for example is able to block the production of toxins when the bacterium is out of the human body. For this, the bacterium uses a "thermostat function” consisting of an RNA molecule that has a condensed structure, blocking protein production at low temperatures. At higher temperatures (e.g. inside of the human body) the RNA molecule opens its structure and allows for production of toxins. By its flexibility, the RNA molecule allows very sophisticated cell signalling not only in bacteria, but also in human cells.

"We have studied different RNA molecules that Listeria requires to be infectious," says Jörgen Johansson, who led the study now being published in the prestigious international journal Cell.

His team has, in a joint study together with colleagues from the Institute Pasteur in Paris and the National Cancer Institute in the United States, discovered a totally new mechanism of a previously known regulatory RNA molecule. This molecule links with another RNA and inhibits its activity in an unprecedented manner. Since these “RNA switches” also occur in eukaryotic cells as well as in other bacteria, the new mechanism that the Umeå researchers have discovered is also significant for other research groups. It shows that the different RNA molecules have more flexibility than known up to now.

"Our results show a more complex network of different regulatory units to ensure that the bacterium only causes disease at the right time," Johansson says.

Article authors Edmund Loh, Jonas Gripenland, Teresa Tiensuu, Karolis Vaitkevicius and Jörgen Johansson (group leader) are working at the Department of Molecular Biology and the group is also affiliated to MIMS (The Laboratory for Molecular Infection Medicine, Sweden) at Umeå University. Most of the work was carried out in Umeå, a smaller part at the Pasteur Institute and the National Cancer Institute.

Original publication:
E Loh, O Dussurget, J Gripenland, K Vaitkevicius, T Tiensuu, P Mandin, F Repoila, C Buchrieser, P Cossart, J Johansson. A trans-Acting Riboswitch Controls Expression of the Virulence Regulator PrfA in Listeria monocytogenes.
Cell 139, November 13, 2009

Contact:Jörgen Johansson, group leader,Department of Molecular Biology andThe Laboratory for Molecular Infection Medicine Sweden
Phone: +46-90-7852535

Editor: Eva-Maria Diehl