Salmonella's Safety Catch

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Science  21 May 2010:
Vol. 328, Issue 5981, pp. 981-982
DOI: 10.1126/science.1190758

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Many pathogenic bacteria disable their host's immune system and thereby protect themselves from destruction by delivering “effector proteins” into the inner, cytosolic compartment of the eukaryotic host cells. Gram-negative bacteria, in particular, have evolved an elaborate “needle complex”—the type III secretion system (T3SS), consisting of more than 20 proteins—to convey an arsenal of effector proteins from their own cytosolic compartment across three membranes directly into the cytosol of the host cell (1). These bacteria spend much of their lives in transit between eukaryotic hosts, however, and it would be a potentially catastrophic waste of their resources to secrete effector proteins continuously into their environment. On page 1040 of this issue, Yu et al. (2) describe a system to regulate the secretion process in Salmonella enterica, an important intracellular pathogen of humans and animals.