A Bacterial Guanine Nucleotide Exchange Factor Activates ARF on Legionella Phagosomes

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Abstract
The intracellular pathogen Legionella pneumophilasubverts vesicle traffic in eukaryotic host cells to create a vacuole that supports replication. The dot/icm genes encode a protein secretion apparatus that L. pneumophila require for biogenesis of this vacuole. Here we show that L. pneumophilaproduce a protein called RalF that functions as an exchange factor for the ADP ribosylation factor (ARF) family of guanosine triphosphatases (GTPases). The RalF protein is required for the localization of ARF on phagosomes containing L. pneumophila. Translocation of RalF protein through the phagosomal membrane is adot/icm-dependent process. Thus, RalF is a substrate of the Dot/Icm secretion apparatus.