containing a domain with Rho-GAP activity (which can inactivate host small GTPases of the Rho/Rac subfamily). During P. aeruginosa infection, ExoS is injected into host cells by a type-II secretion system (TTSS), and infection of flies with P. aeruginosa leads to rapid death that depends on TTSS function (Fauvarque et al., 2002) . When the GAP domain of ExoS (ExoSGAP) is expressed in fly hemocytes, phagocytosis is inhibited (Avet-Rochex et al., 2005) . In addition, expression of ExoSGAP in flies increases their sensitivity to infection by P. aeruginosa (Avet-Rochex et al., 2005) , and this effect can be rescued by co-expressing host Rac2 with ExoSGAP (Avet-Rochex et al., 2007) . These studies provide evidence that host Rac2 is inhibited by bacterial ExoSGAP during infection.