May have dual functions, one in vegetative cells at starvation involving cell-type choice and a later function involving progression to the tipped mound stage. Involved in vesicle fusion in endo- and exocytosis. Involved in L.pneumophila intracellular growth. Mostly found in the cytosol but also found associated with both small organelles or vesicles. Expressed in vegetative cells. Levels decrease dramatically as development begins, and remain low throughout the aggregation and loose mound stages. The levels become more abundant again at the tight-mound stage and remain high throughout the rest of development and fruiting body formation. Rapidly up-regulated by hyperosmotic stress, which is dependent on dstC. Strongly inducible by 8-bromo-cGMP and to a lesser extent by 8-bromo-cAMP. Not induced by DIF (differentiation-inducing factor, a chlorinated hexaphenone). Up-regulated following Legionella pneumophilia infection. Aberrant ratio of prespore to prestalk cells. Cells stall and only 10% of the aggregates form fruiting bodies. The fruiting bodies that do form have abnormal shapes, with enlarged stalks and aberrantly small mass of spores. Cells also show a decreased exocytosis rate, decreased pH of endocytic vesicles, lack of morphologically distinguishable post-lysosomal compartments as well as perturbation of the cell cycle-regulated cytosolic pH. Cells infected with Legionella pneumophilia are defective for maturation of the L.pneumophilia replication vacuole.